Body temperature
The body's warmth in degrees Celsius, one of the basic vital signs
Also known as
Definition
Body temperature is one of the vital signs, along with pulse, breathing rate and blood pressure. The average normal value is taken to be 37 °C. It varies, however, by person, age, activity and time of day: in adults it is lowest in the early morning and usually highest in the evening. Where it is measured also affects the result. A measurement can help detect illness and follow its course.
| Parameter | Value |
|---|---|
| Unit | °C (in the US °F) |
| Reference Range | At rest in adults about 36.5–37.3 °C, average 37 °C; another MedlinePlus page gives 36.1–37.2 °C. Values vary over the day and with the measuring site and device. If a medical report gives its own range, that range is what counts; your doctor interprets the result. |
Agree on your personal target range with your doctor.
Conversion: °F = °C × 1.8 + 32. Examples: 35 °C = 95 °F, 37 °C = 98.6 °F, 38 °C = 100.4 °F.
↓ What a low value means
Temperature is naturally lowest in the early morning, and readings in the armpit or on the forehead are usually 0.3–0.6 °C lower than a reading in the mouth. A dangerously low body temperature below 35 °C is called hypothermia. It occurs when the body loses more heat than it makes, mostly after long periods in the cold, in wet clothing or after falling into cold water. People at particular risk are the very old and very young, the chronically ill, the malnourished and people under the influence of alcohol, drugs or certain medicines. Confusion, drowsiness, pale cold skin and uncontrollable shivering are an emergency. Some serious infections can come with a very low temperature, most often in infants.
↑ What a high value means
A temperature above 38 °C most often means a fever caused by an infection or illness. An adult probably has a fever when the reading in the mouth is above 37.2–37.5 °C, depending on the time of day. Fever is part of the body's defense against infection. Besides infections, it can be linked to inflammatory and autoimmune diseases, blood clots, some medicines and certain cancers. Without illness, activity, strong emotions, eating, heavy clothing, heat and high humidity, and the second half of the menstrual cycle also raise temperature. Adults should seek medical advice at 40.6 °C or higher, with a fever that stays at or above 39.4 °C, or with a fever lasting longer than 48–72 hours.
When to test
When there are signs of illness or to follow the course of an illness. Electronic thermometers are most often recommended: in the mouth for about 3 minutes, in the armpit for about 5 minutes or until the device beeps. Wait 1 hour after heavy exercise or a hot bath, and 20–30 minutes after smoking, eating or a hot or cold drink. Mention the measuring site when you report a fever. Strip thermometers measure skin temperature, not body temperature; wearable readings do not replace a thermometer measurement.
Frequently asked questions
Is 37 °C the normal value for everyone? +
37 °C is taken as the average normal value. Normal temperature differs from person to person, though, and varies with age, activity and time of day. Studies show a range of about 36.1 to 37.2 °C.
When is it considered a fever? +
A temperature above 38 °C most often means a fever. In adults, a fever is probably present once the reading in the mouth is above 37.2 to 37.5 °C, depending on the time of day. A reading about 0.6 to 0.8 °C above your own usual temperature is also considered a fever.
Why do readings in the mouth, ear and armpit differ? +
As a rough guide, a rectal or ear reading is 0.3 to 0.6 °C higher than a reading in the mouth, and an armpit or forehead reading is 0.3 to 0.6 °C lower. The exact relationship is not clear. So compare readings from the same measuring site.
Does the menstrual cycle change body temperature? +
Yes. In the second half of the cycle, temperature can rise by about 0.6 °C (1 °F) or more. This is one of the normal influences on body temperature, like time of day, activity and eating.
Body temperature
Sources
Last updated: October 05, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.