Body Temperature °F to °C: Fever Chart and Conversion

The short answer

To convert a body temperature from Fahrenheit to Celsius, subtract 32 and multiply by 5/9. So 100.4 °F is 38 °C, which is the usual fever threshold used by the NHS and the US CDC. A reading of 98.6 °F is 37 °C. Type any thermometer reading into the Temperature Converter to get the exact value in °C, °F and Kelvin.

This page is about converting numbers. It is not medical advice. If you are worried about someone's temperature or symptoms, contact a doctor or your local health service.

Body temperature chart: °F to °C

These values are rounded to one decimal place, which is how most digital thermometers display them.

Fahrenheit	Celsius	What it usually means
97.0 °F	36.1 °C	Within the normal range for many people
98.0 °F	36.7 °C	Normal range
98.6 °F	37.0 °C	The traditional "normal" figure
99.0 °F	37.2 °C	Normal to slightly raised
99.5 °F	37.5 °C	Slightly raised
100.0 °F	37.8 °C	Raised, below the usual fever threshold
100.4 °F	38.0 °C	Usual fever threshold
101.0 °F	38.3 °C	Fever
102.0 °F	38.9 °C	Fever
103.0 °F	39.4 °C	Fever
104.0 °F	40.0 °C	High fever
105.0 °F	40.6 °C	High fever

Celsius to Fahrenheit chart

If your thermometer shows Celsius and the advice you are reading uses Fahrenheit, use this table instead.

Celsius	Fahrenheit
36.0 °C	96.8 °F
36.5 °C	97.7 °F
37.0 °C	98.6 °F
37.5 °C	99.5 °F
38.0 °C	100.4 °F
38.5 °C	101.3 °F
39.0 °C	102.2 °F
39.5 °C	103.1 °F
40.0 °C	104.0 °F
41.0 °C	105.8 °F

What counts as a fever

Two widely used public health sources give the same threshold:

• The NHS says a high temperature is usually considered to be 38 °C or above.
• The US CDC defines fever as a measured temperature of 100.4 °F (38 °C) or greater, or feeling warm to the touch or reporting feeling feverish.

The NHS also points out that normal body temperature is different for everyone and changes during the day, so there is no single "normal" number. The 98.6 °F (37 °C) figure is a convenient reference, not a target everyone should hit.

How to convert a reading yourself

Fahrenheit to Celsius

Subtract 32 from the Fahrenheit reading.

Multiply the result by 5.

Divide by 9.

Example: 102 °F. 102 − 32 = 70. 70 × 5 = 350. 350 ÷ 9 = 38.89, so about 38.9 °C.

Celsius to Fahrenheit

Multiply the Celsius reading by 9.

Divide by 5.

Add 32.

Example: 38.5 °C. 38.5 × 9 = 346.5. 346.5 ÷ 5 = 69.3. 69.3 + 32 = 101.3 °F.

Quick mental check

Each 1 °C step is 1.8 °F. So if 37 °C is 98.6 °F, then 38 °C is 98.6 + 1.8 = 100.4 °F, and 39 °C is 102.2 °F. This is a handy way to sanity-check a conversion without a calculator.

Using the Temperature Converter

Open the Temperature Converter. It starts with Celsius to Fahrenheit selected.

Type the reading in the value box, for example 37.8.

Read the result in the "to" box, here 100.04 °F.

To go the other way, press the swap button or change the "From" menu to Fahrenheit.

The list underneath shows the same value in all three units, including Kelvin, and you can click a row to copy it.

The converter shows up to six decimal places. Thermometers round to one, so round the answer the same way before comparing it with a chart. For example, 101 °F converts to 38.333333 °C, which you would read as 38.3 °C.

Common mistakes when converting body temperature

• Forgetting to subtract 32 first. Multiplying 100.4 by 5/9 gives 55.8, which is obviously wrong for a body temperature. Always subtract 32 before multiplying.
• Using 2 instead of 1.8. The "double and add 30" shortcut works for weather, but it is not accurate enough for body temperature. 38 °C becomes 106 °F with that shortcut, instead of the correct 100.4 °F.
• Comparing different measuring sites. Readings taken under the tongue, in the armpit, in the ear or on the forehead can differ. Follow the instructions for your thermometer, and compare readings taken the same way.
• Over-reading the decimals. The difference between 37.4 °C and 37.5 °C is within normal variation and measurement error. Look at the overall reading and how the person feels.
• Assuming a normal reading rules out illness. The NHS notes that if you feel hot or cold you may have a high temperature even if a thermometer reads below 38 °C.

Checking a temperature properly

The NHS gives this practical guidance for adults:

• Use a digital thermometer, placing the tip under the tongue or, alternatively, in the armpit, and follow the device's instructions.
• Do not use glass thermometers, infrared thermometers or forehead strips.
• You can also look for signs such as the chest or back feeling hotter than usual, feeling shivery, or sweating.

For babies and children, thresholds and advice differ by age, so follow guidance written for children from your doctor or national health service.

When to get help

The NHS advises asking for an urgent GP appointment or contacting NHS 111 if you have a high temperature that is not getting better or is getting worse after treating it at home. Outside the UK, contact your doctor or local health service. Seek emergency care for severe symptoms such as difficulty breathing, confusion or a seizure.

Other conversions you might need

• Oven temperatures, including fan ovens and gas marks: see Oven Temperature Conversion.
• Weather and general temperatures: see Celsius to Fahrenheit Conversion.
• Body weight in kg and lbs for medicine labels or health forms: use the Weight Converter.