What is considered a high fever in adults. How can you treat a fever at home. When should you worry about a fever. What are the common causes and symptoms of fever in adults. How do doctors diagnose the underlying cause of a fever.

Understanding Fever: Definition and Temperature Ranges

Fever is a crucial defense mechanism employed by the body to combat infections. It occurs when the body temperature rises above the normal range, making it more difficult for infectious agents like viruses and bacteria to thrive. But what exactly constitutes a fever?

The average body temperature is generally considered to be 98.6°F (37°C). However, it’s important to note that “normal” body temperature can vary from person to person and fluctuate throughout the day. A temperature reading of 100.4°F (38°C) or higher is typically classified as a fever in adults.

Fever Severity Levels

• Low-grade fever: 99.1°F to 100.4°F (37.3°C to 38.0°C)
• Moderate-grade fever: 100.6°F to 102.2°F (38.1°C to 39.0°C)
• High-grade fever: 102.4°F to 105.8°F (39.1°C to 41°C)

Understanding these temperature ranges can help you assess the severity of your fever and determine when to seek medical attention.

Common Causes of Fever in Adults

While infections are the most frequent culprits behind fevers, various other conditions can also elevate body temperature. Identifying the underlying cause is crucial for appropriate treatment.

Infectious Causes

• Viral infections (e.g., influenza, COVID-19)
• Bacterial infections (e.g., strep throat, urinary tract infections)
• Fungal infections
• Parasitic infections

Non-Infectious Causes

• Inflammatory conditions (e.g., rheumatoid arthritis)
• Reactions to medications or vaccines
• Certain types of cancers
• Heat exhaustion or heatstroke
• Hormonal imbalances

Can stress cause a fever? While stress itself doesn’t directly cause fever, prolonged stress can weaken the immune system, making you more susceptible to infections that may lead to fever.

Recognizing Fever Symptoms and Warning Signs

Fever often comes with a constellation of symptoms that can help you identify its presence and severity. Being aware of these symptoms can guide you in deciding whether to seek medical attention.

Common Fever Symptoms

• Sweating or chills
• Headache
• Muscle aches
• Loss of appetite
• Fatigue or weakness
• Dehydration
• Irritability

How can you tell if you have a fever without a thermometer? While a thermometer provides the most accurate reading, some signs that may indicate a fever include feeling unusually warm to the touch, experiencing chills, or noticing flushed skin.

Red Flags: When to Seek Immediate Medical Attention

Certain symptoms accompanying a fever warrant immediate medical evaluation:

• Seizures
• Loss of consciousness
• Confusion or altered mental state
• Stiff neck
• Difficulty breathing
• Severe pain in any part of the body
• Swelling or inflammation
• Unusual vaginal discharge or urinary symptoms

If you experience a fever above 104°F (40°C) or any of these warning signs, it’s crucial to seek medical help promptly.

Diagnosing the Underlying Cause of Fever

When you visit a healthcare provider with a fever, they will conduct a thorough evaluation to determine its root cause. This process typically involves several steps to gather essential information.

Medical History and Symptom Assessment

Your doctor will likely ask about:

• Recent illnesses or infections
• Travel history, especially to areas with endemic diseases
• Current medications and recent vaccinations
• Chronic health conditions
• Specific symptoms accompanying the fever

Physical Examination

A comprehensive physical exam may include:

• Checking vital signs (temperature, heart rate, blood pressure, respiratory rate)
• Examining the throat, ears, and lymph nodes
• Listening to heart and lung sounds
• Palpating the abdomen for any tenderness or swelling

Diagnostic Tests

Depending on the suspected cause, your doctor may order various tests:

• Blood tests (complete blood count, metabolic panel, blood cultures)
• Urine analysis
• Throat or nasal swabs
• Imaging studies (X-rays, CT scans, or MRI)
• Specialized tests for specific infections or conditions

How long does it take to diagnose the cause of a fever? The time frame can vary significantly depending on the complexity of the case and the tests required. Some causes may be identified within hours, while others might take several days or longer to pinpoint accurately.

Effective Home Remedies for Fever Management

While fever itself is often a beneficial response to infection, managing its symptoms can provide comfort and prevent complications. Here are some effective home remedies to help alleviate fever symptoms:

Hydration is Key

Maintaining proper hydration is crucial when dealing with a fever. Increased body temperature leads to more rapid fluid loss through sweating and increased metabolism.

• Drink plenty of water, clear broths, or electrolyte solutions
• Avoid caffeine and alcohol, which can contribute to dehydration
• Consume cool or room temperature fluids rather than very cold ones

Rest and Recovery

Allowing your body to rest is essential for recovery:

• Get plenty of sleep
• Avoid strenuous activities
• Create a comfortable, cool environment for resting

Dietary Considerations

While you may not feel very hungry, maintaining nutrition is important:

• Eat light, easily digestible foods
• Consider soups, broths, and fruit juices for hydration and nutrients
• Avoid heavy, greasy, or spicy foods that may be hard to digest

Over-the-Counter Medications

Certain medications can help reduce fever and alleviate associated symptoms:

• Acetaminophen (Tylenol)
• Ibuprofen (Advil, Motrin)
• Naproxen (Aleve)

Always follow the recommended dosage and consult with a healthcare provider if you have any concerns or underlying health conditions.

Cool Compresses and Lukewarm Baths

External cooling methods can provide relief:

• Apply a cool, damp washcloth to the forehead, wrists, or back of the neck
• Take a lukewarm bath or shower (avoid cold water, which can cause shivering and potentially raise body temperature)

Is it better to cover up or uncover when you have a fever? While it may seem counterintuitive, keeping yourself covered with a light blanket can actually help regulate body temperature. If you’re experiencing chills, cover up, but remove layers if you start to feel too warm.

When to Seek Professional Medical Care for Fever

While many fevers can be managed at home, certain situations require professional medical attention. Knowing when to seek help is crucial for preventing potential complications and ensuring proper treatment.

Age and Risk Factors

Certain groups should be more cautious about fevers:

• Adults over 65
• Individuals with weakened immune systems
• People with chronic health conditions (e.g., heart disease, diabetes, lung disease)
• Pregnant women

These groups should consult a healthcare provider even for milder fevers, as they may be at higher risk for complications.

Temperature Thresholds

Seek medical attention if:

• Your fever reaches 103°F (39.4°C) or higher
• You have a fever above 101°F (38.3°C) that lasts for more than three days
• Your fever doesn’t respond to over-the-counter medications

Accompanying Symptoms

Certain symptoms in conjunction with fever warrant immediate medical evaluation:

• Severe headache or neck stiffness
• Confusion or altered mental state
• Difficulty breathing or chest pain
• Severe abdominal pain
• Persistent vomiting or diarrhea
• Unusual skin rashes or bruising

How quickly should a fever respond to treatment? If your fever doesn’t show improvement within 48 to 72 hours of home treatment, or if it worsens despite your efforts, it’s time to consult a healthcare provider.

Potential Complications of Untreated High Fever

While fever itself is often a beneficial immune response, prolonged or extremely high fevers can lead to complications if left untreated. Understanding these potential risks underscores the importance of proper fever management and timely medical intervention when necessary.

Dehydration

One of the most common complications of fever is dehydration. High body temperature increases fluid loss through sweating and elevated metabolism. Severe dehydration can lead to:

• Electrolyte imbalances
• Decreased blood volume
• Organ stress, particularly on the kidneys
• In extreme cases, shock

Neurological Effects

Very high fevers, particularly those above 104°F (40°C), can affect the nervous system:

• Febrile seizures (more common in children but can occur in adults)
• Confusion or delirium
• Hallucinations

Metabolic Stress

Prolonged high fever increases the body’s metabolic rate, which can lead to:

• Increased protein breakdown
• Muscle wasting
• Nutritional deficiencies

Cardiovascular Strain

High fever can put additional stress on the cardiovascular system:

• Increased heart rate
• Elevated blood pressure
• Potential exacerbation of existing heart conditions

Can a high fever cause permanent damage? While rare, extremely high fevers (above 106°F or 41.1°C) or prolonged high fevers can potentially cause organ damage, particularly to the brain. This underscores the importance of managing high fevers and seeking medical attention when appropriate.

Exacerbation of Underlying Conditions

For individuals with pre-existing health conditions, a high fever can worsen their overall health status:

• Aggravation of respiratory conditions like asthma or COPD
• Increased difficulty managing diabetes
• Potential complications for those with autoimmune disorders

Prevention Strategies: Reducing Your Risk of Fever-Causing Illnesses

While it’s not always possible to prevent fever, many strategies can help reduce your risk of contracting infections that commonly cause fevers. Implementing these preventive measures can contribute to overall health and well-being.

Hygiene Practices

Maintaining good hygiene is crucial in preventing the spread of infectious agents:

• Wash hands frequently with soap and water for at least 20 seconds
• Use alcohol-based hand sanitizers when soap and water are unavailable
• Avoid touching your face, especially your mouth, nose, and eyes
• Cover your mouth and nose when coughing or sneezing

Vaccination

Staying up-to-date with recommended vaccinations can prevent many fever-causing illnesses:

• Annual flu shots
• COVID-19 vaccines and boosters
• Routine adult vaccinations (e.g., tetanus, pneumococcal)
• Travel-specific vaccines when visiting certain regions

Healthy Lifestyle Choices

A strong immune system is your best defense against infections:

• Maintain a balanced diet rich in fruits, vegetables, and whole grains
• Stay physically active with regular exercise
• Get adequate sleep (7-9 hours for most adults)
• Manage stress through relaxation techniques or mindfulness practices
• Limit alcohol consumption and avoid smoking

Environmental Awareness

Being mindful of your surroundings can help reduce exposure to pathogens:

• Avoid close contact with individuals who are sick
• Be cautious in crowded, poorly ventilated spaces during flu season
• Practice food safety by properly handling and cooking foods
• Use insect repellent and protective clothing in areas with vector-borne diseases

How effective are these prevention strategies in reducing fever risk? While no method is 100% foolproof, consistently practicing these preventive measures can significantly reduce your risk of contracting infections that cause fever. Studies have shown that proper hand hygiene alone can reduce the risk of respiratory infections by up to 21%.

Regular Health Check-ups

Maintaining regular contact with your healthcare provider can help prevent and detect issues early:

• Schedule annual physical exams
• Stay current with health screenings appropriate for your age and risk factors
• Discuss any health concerns or changes with your doctor promptly

By incorporating these preventive strategies into your daily routine, you can create a robust defense against many fever-causing illnesses. Remember, prevention is always preferable to treatment, and these habits contribute to overall health beyond just fever prevention.

Fever in adults – Harvard Health

Fever is one of the body’s most effective ways of fighting infection. It is part of your body’s defense against infection-causing germs.

You get a fever most often when your body is trying to kill infectious invaders such as viruses or bacteria. A higher body temperature helps the immune system respond more vigorously to the attack, and makes it harder for these microbes to survive.

What is considered a fever in adults?

The average body temperature is 98.6° F (37°C). But “normal” body temperature varies from person to person. It also changes during the day, rising a bit after you eat or exercise. Body temperature is often higher in the afternoon than it is when you wake up in the morning.

Fever means a body temperature of 100.4° F (38°C) or higher.

High fever in adults

While any temperature above your normal temperature range is considered a fever, there are different levels of fever severity:

• Low-grade: 99. 1 to 100.4 F (37.3 to 38.0 C)
• Moderate-grade: 100.6 to 102.2 F (38.1 to 39.0 C)
• High-grade: 102.4 to 105.8 F (39.1 to 41 C)

When to worry about fever

If you have a fever over 104°F (40°C), you should call your doctor.

Seek medical help right away if you have a fever along with any of these symptoms:

• seizure
• loss of consciousness
• confusion
• stiff neck
• trouble breathing
• severe pain anywhere in the body
• swelling or inflammation of any part of the body
• vaginal discharge that is discolored or smells bad
• pain when urinating or urine that smells bad.

Causes of fever

An infection, such as the flu, is the most common cause of fever.

Other conditions can also cause a fever. These include diseases that produce inflammation, such as rheumatoid arthritis; reactions to drugs or vaccines; and even certain types of cancers.

Accompanying symptoms

The following symptoms may also accompany fever:

• sweats
• chills
• headache
• achy muscles
• lack of desire to eat
• rash
• restlessness
• weakness.

A very high fever can cause confusion, extreme sleepiness, irritability, and seizures.

Diagnosing the cause of a fever

To help determine why you have a fever, your doctor will ask you about:

• other symptoms such as coughing, abdominal pain, vomiting, diarrhea, or pain when urinating
• recent surgeries or injuries
• recent vaccinations
• new drugs you may be taking
• recent travel, particularly travel abroad.

How to treat a fever at home

By itself, fever is usually harmless, though a high fever can be miserable. These steps may help you feel better:

• Drink plenty of fluids to help cool your body and prevent dehydration.
• Eat light foods that are easy to digest.
• Get plenty of rest.
• Take ibuprofen (Advil, Motrin, or others), naproxen (Aleve, Naprosyn, or others), or acetaminophen (Tylenol, others) to help relieve head and body aches and lower your temperature.
• Take a slightly warm (not cool) bath, or apply damp washcloths to the forehead and wrists.

Image: yacobchuck/Getty Images

Treat High Fever in Children and Adults

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The Urgency Room is your comprehensive one-stop location for your urgent needs. Our standalone facilities are expertly outfitted with emergency trained providers and  state-of-the-art equipment to handle the variety of aches, pains, breaks, and illnesses that come through our doors every day.

Schedule an appointment at any of our three locations, open 365 days a year, including holidays, from 8:00 AM to 9:00 PM. Our telehealth services are available from 8:00 AM to 8:00 PM. Situated in Woodbury, Vadnais Heights, and Eagan, The Urgency Room is the quick and convenient alternative to overcrowded and understaffed emergency rooms for residents throughout the Twin Cities.

If you or your child has a high fever, don’t hesitate to seek care. Don’t drudge through hours of waiting at your typical emergency room. Instead, get evaluated and treated at your nearest Urgency Room, fast. With short wait times, friendly staff, and highly experienced providers, you’ll be back to yourself in no time.

What Is Considered a High Fever in Adults?

Most adults have a baseline temperature of 98. 6 F. Generally, temperatures of 103 degrees Fahrenheit or higher are considered high for an adult. However, when an adult sustains a temperature higher than 100 degrees Fahrenheit for an unusually long period of time, it could also be cause for concern. It’s best to act on the safe side and seek care at The Urgency Room right away. Fevers can be very complex and can stem from many different types of illnesses or infections. The providers at The Urgency Room can accurately assess and diagnose the source of your high fever. 

Fevers occur when the hypothalamus, your body’s “thermostat,” increases your body’s temperature because of fever-producing substances called pyrogens. When pyrogens are released into your blood, you could wind up with a dangerously high fever. Pyrogens could come from bacteria, drugs, toxins, viruses, and fungi. The severity of fever and its detrimental results increase as your condition persists—which is why getting a high fever treated sooner is always your best option.  

High Fever Thresholds 

Once a fever goes beyond the high level, an adult enters dangerous fever levels (104 F – 107 F). This dangerous level, also known as hyperpyrexia, is considered a medical emergency and you should seek medical care immediately. 

To give you a rough idea of the fever levels in adults, here’s a list: 

• Low high fever: 100 F – 101 F
• Intermediate high fever: 102 F
• Serious high fever: 103 F – 104 F
• Hyperpyrexia: 104 F – 107 F

It is sometimes difficult to pinpoint the source of a fever as there are an incredible number of diseases and illnesses that have high temperatures as a side effect or symptom. And while fevers most frequently accompany a viral illness, our providers will try and get down to the exact source. 

What Is Considered a High Fever in Children?

A high fever in a child may be any temperature higher than 100 degrees Fahrenheit, especially if that temperature is sustained above the 100-degree threshold for extended periods. If your child’s temperature is not showing signs of reducing, you should seek emergency care.

The severity and damage a fever can cause vary by the age of the child. Younger children and infants should be seen by a medical provider sooner than an adult or teenager would with a similar temperature.

In addition to high or rising temperatures that last longer than 24 hours, a child with a high fever could have other obvious symptoms. Be on the lookout for severe diarrhea, dehydration, repeated vomiting, seizures, or rash. Your child is especially susceptible to serious infections if they have any type of immune disorder or haven’t received immunizations.

When minutes matter, especially if your child has a high fever, get to your nearest Urgency Room—we have shorter wait times and state-of-the-art equipment to treat your illness fast.        

When Is It Time to Seek Care?

As listed above, the duration one with a high fever should wait to seek medical treatment varies depending on age. An infant should be seen right away even if it has temperatures constituting a low fever in adults. Similarly, an adult can wait until the fever persists for a day or two while a child, depending on its age, should be seen as soon as they’ve had a fever of any temperature for longer than 24 hours.

You may try fever-reducing medicines (ones containing acetaminophen) before seeking medical care, however, always consult with a medical provider if you are uncertain what medicine to administer for your child. 

Consider Using Telehealth for Less Intense Fevers

If you’re not experiencing a medical emergency but you’re concerned about your fever level or that of your child, consider using online care services. The Urgency Room utilizes video technology for patient convenience and overall experience improvement. You won’t have to waste precious time in your vehicle or using public transportation, not to mention waiting in the lobby. Just follow the instructions on our Online Care page.

How Can The Urgency Room Treat High Fevers in Adults and Children?

The Urgency Room is well-equipped to take care of you or your child when experiencing a high fever. Prolonged fever or dangerously high fevers can cause an onslaught of residual health problems, so it is always best to seek care rather than ignore the problem.

All three Urgency Room locations are equipped with providers and staff who have extensive emergency room experience as well as equipment to assess, diagnose and treat your illness or injury. 

Up-to-date technology at our Urgency Room locations includes:

• X-ray machines
• CT scanner
• Ultrasound
• High-complexity lab
• Sedation for adults and children

The Urgency Room also has a large library of at-home aftercare videos for you to reference after you’ve left our in-person care. Before, during, and after illness, The Urgency Room has your well-being as our first priority.

Medical  Care for a Wide Range of Symptoms, Available In-Person or Online

Looking for fast, trusted medical care in the Twin Cities? The Urgency Room can help you avoid the crowds and long waits of typical emergency rooms. Our facilities are owned and operated by members of the Emergency Physicians Professional Association. Our board-certified physicians and staff are here for you when you need medical care the most. 

We’ll always provide you with exceptional medical care closer to home. Schedule your non-emergent visits or log in online to start a visit with one of our providers online.

Body temperature

Well, who said that your ideal temperature is 36.6 ° C? And if the thermometer is 35.4 or 37.2 ° C and you feel good at the same time? Is it worth it in this case to sound the alarm, swallow packs of pills for prevention and run to the hospital?
The body temperature of a young healthy person ranges from 36.2 to 36.8 °C. And only for 5% of people are normal indicators below or above the average. That is why some, for whom the lower limits are characteristic, “almost die” at 37.2 ° C, while others simply do not notice such a slight increase.
You can find out what the norm is for you personally if you measure your temperature in the morning, afternoon and evening if you feel well. After all, during the day it changes: the lowest is before noon, when the body is still sleeping, then it gradually rises and reaches a maximum by about 4 pm.

How to measure temperature correctly?

The temperature of the skin is not the same in different parts of the body, for example, on the foot – only about 20 °C. In sports medicine, there is the concept of weighted average skin temperature (WTC), which is measured at five points (in the forehead, chest, hand, thigh and lower leg).
The most common “home” way to find out the temperature is to put a thermometer under your arm. But it is the least reliable. The temperature in the mouth fluctuates depending on the cold or hot food eaten. It is best to put a thermometer, and only electronic, in the ear or rectum.
If you don’t have a thermometer handy, try to determine the temperature by touching your forehead with your lips or the back of your hand.

What can influence the temperature?

First of all – the individual characteristics of the organism. As a rule, people with a slow metabolism have a lower temperature than those with a stable and high metabolism. But if, despite feeling good, you continue to worry about your body temperature being too low, try a school favorite method: put a few drops of iodine on a sugar cube and eat it. If the thermometer creeps up, then everything is in order: the body is working properly, and low readings are your norm.

Factors affecting a woman’s temperature:

Menstrual cycle. 2 weeks before it starts, as a rule, it decreases, and on the first day it increases.
Pregnancy. For no apparent reason, for several months it is increased by several tenths of a degree in 30% of expectant mothers.
Smoking. Nicotine interferes with normal blood circulation, reduces the supply of oxygen to the vessels. These deviations in the system lead to a decrease in body temperature.
Age. Over time, she may change her “healthy” indicators. By the age of 65, they often decrease by 1-2 °. There are some advantages to this: for example, it becomes easier for women to endure the sweltering heat.
Genetics, lifestyle, environment. True, the significance of these factors is not so great.

Our body has the ability to maintain a constant body temperature. Neither the African heat nor the Russian cold can shake it. He possesses this feature thanks to a special organ located in the cerebral cortex – the hypothalamus. It is he who controls the heat balance of a person.
If we are hot, the vessels dilate, passing more blood, the skin heats up, sweating increases, as a result of which the temperature drops. If it is cold outside, the vessels, on the contrary, narrow, the skin remains cold and does not give off heat. By the way, the same hypothalamus makes us shiver when it’s cold. We tremble – and warm up. A person spends a huge amount of energy to maintain the thermal balance, thanks to which he can be active and vital at any time of the year. Without this ability, people would be forced to roam all the time after good weather.

Temperature and sports

During sports, metabolic processes are activated, cardiac output, blood minute volume, its flow to the skin increase … Such changes lead to an increase in temperature. During normal training, it is small – a few tenths of a degree. In addition, our brain quickly compensates for the costs of habitual exercises and brings the indicators back to normal. Another thing is extreme loads, when the recovery process takes longer, since the changes are very significant. For example, marathon runners have a body temperature of 38.9 at the finish line.°C regardless of the weather. If you dared to run such a race, then the thermometer could rise to 40 ° C and above. It’s just that professional athletes have better thermoregulation mechanisms than ordinary people. In other words, they begin to sweat when there is still plenty of strength left. And an amateur often already suffocates, but at the same time remains completely dry, which is harmful to the body.

Abnormalities

There are situations in which the hypothalamus, which is responsible for maintaining heat balance, needs outside help. Fever is one of the ways the body fights infection, when the inflammatory process ends with the release of blood from unnecessary chemical elements at the cellular level. But if the elevated temperature does not fall below 38.5 ° C for several days, it is necessary to start taking some kind of antipyretic, because the internal organs of a person cannot function for a long time at a high temperature.
The body also needs help when the temperature drops to 35 ° C, which happens due to prolonged hypothermia (hypothermia). In this case, a warm drink and warm clothing are needed. A slight decrease in temperature can also be observed in the post-traumatic period, as well as in elderly people due to low activity or malnutrition.
Often, critical changes in body temperature are caused by inadequate behavior of the person himself. Follow the advice: always dress appropriately for the weather, do not sit in the steam rooms and do not jump into the hole as soon as you decide to become a walrus.

Interesting facts

The highest temperature – 46.5 ° C – was registered in 52-year-old American Willie Jones in 1980. He suffered heatstroke and was taken to the hospital. He was discharged 24 days later in a satisfactory condition. The lowest temperature – the Russian Viktor Kharin in 1960. They found him outside on a frosty night. The protocol says: “A numb body in icy clothes. When tapped, a dull sound is heard, as from blows on wood. The body surface temperature is below 0 °C, signs of life are not determined. Diagnosis: general freezing, clinical death. When the victim was placed in a hot bath and resuscitation began, after 1.5 hours he developed weak breathing and a pulse. For 12 hours, the body temperature of the man rose to 36 ° C.

There is a special method of treatment – pyrotherapy (from the Greek “fire”), when a person is specially injected with pyrogens – substances that cause fever. The feverish state is accompanied by the activity of the pituitary-adrenal system, the acceleration of blood flow in the internal organs by 2-3 times, and the stimulation of the immune system. At such a high temperature, blood clots dissolve more efficiently, dense scar tissue dissolves, degenerate tumor cells die, and the activity of the nervous system is restored.

The need to introduce a single temperature scale arose at the beginning of the 18th century – by that time there were already more than 30 of them. The German physicist Gabriel Daniel Fahrenheit and the Swedish astronomer and physicist Anders Celsius, who was the first to manufacture alcohol and mercury thermometers, took up this task. Both proceeded from the fact that 1 degree is equal to the difference between the temperatures of boiling water and melting ice at atmospheric pressure. But everyone defined the points of melting ice and boiling water in their own way: Celsius as 1/100, Fahrenheit as 1/180. Both scales “took root” and are still used today.

Temperature scale. Celsius, Fahrenheit, Kelvin, Réaumur

History

The word “temperature” arose in those days when people believed that hotter bodies contained a greater amount of a special substance – caloric than less heated ones. Therefore, temperature was perceived as the strength of a mixture of body substance and caloric. For this reason, the units of measure for the strength of alcoholic beverages and temperature are called the same – degrees.

From the fact that temperature is the kinetic energy of molecules, it is clear that it is most natural to measure it in energy units (ie in the SI system in joules). However, temperature measurement began long before the creation of molecular kinetic theory, so practical scales measure temperature in conventional units – degrees.

Kelvin scale

Thermodynamics uses the Kelvin scale, in which the temperature is measured from absolute zero (the state corresponding to the minimum theoretically possible internal energy of the body), and one kelvin is equal to 1/273.16 of the distance from absolute zero to the triple point of water (the state at where ice, water and water vapor are in equilibrium). The Boltzmann constant is used to convert kelvins to energy units. Derived units are also used: kilokelvin, megakelvin, millikelvin, etc.

Celsius scale

In everyday life, the Celsius scale is used, in which the freezing point of water is taken as 0, and the boiling point of water at atmospheric pressure is taken as 100 °. Since the freezing and boiling points of water are not well defined, the Celsius scale is currently defined in terms of the Kelvin scale: degrees Celsius equals Kelvin, absolute zero is taken to be -273.15 °C. The Celsius scale is practically very convenient, since water is very common on our planet and our life is based on it. Zero Celsius is a special point for meteorology, since the freezing of atmospheric water changes everything significantly.

Fahrenheit

In England and especially in the USA, the Fahrenheit scale is used. This scale is divided by 100 degrees from the temperature of the coldest winter in the city where Fahrenheit lived to the temperature of the human body. Zero degrees Celsius is 32 degrees Fahrenheit, and a degree Fahrenheit is 5/9 degrees Celsius.

The current definition of the Fahrenheit scale is that it is a temperature scale where 1 degree (1°F) equals 1/180 of the difference between the boiling point of water and the melting point of ice at atmospheric pressure, and the melting point of ice is +32°F. The temperature on the Fahrenheit scale is related to the temperature on the Celsius scale (t ° C) by the ratio t ° C \u003d 5/9(t °F – 32), that is, a change in temperature of 1 °F corresponds to a change of 5/9 °C. Proposed by G. Fahrenheit in 1724.

Reaumur scale

Proposed in 1730 by R. A. Reaumur, who described the alcohol thermometer he invented.

Unit – degree Réaumur (°R), 1 °R is equal to 1/80 of the temperature interval between the reference points – the temperature of melting ice (0 °R) and boiling water (80 °R)

1 °R = 1.25 °C

The scale is now out of use, it has been preserved for the longest time in France, the author’s homeland.

Comparison of temperature scales

¹ Normal human body temperature is 36.6°C ±0.7°C, or 98.2°F ±1.3°F. The commonly quoted value of 98.6 °F is an exact Fahrenheit conversion of the 19th century German value of 37 °C. Since this value does not fall within the range of normal temperature according to modern concepts, we can say that it contains excessive (incorrect) accuracy. Some values ​​in this table have been rounded.

Comparison of Fahrenheit and Celsius scales