Convert Body Temperature from Fahrenheit to Celsius

Direct answer

Subtract 32 from the Fahrenheit body-temperature reading and multiply the result by 5/9.

For example, 98.6°F converts as follows:

Use the Fahrenheit to Celsius Converter for another thermometer reading.

How to convert a thermometer reading

1. Record the complete Fahrenheit value. Include every decimal digit displayed by the thermometer.
2. Subtract 32. Keep the complete intermediate value.
3. Multiply by 5 and divide by 9.
4. Round the final result appropriately. One decimal place is common for many thermometer displays.
5. Label the result in degrees Celsius.

Common body-temperature conversions

These are unit conversions only. The meaning of a reading can depend on age, measurement location, thermometer type, symptoms, timing, and professional guidance.

Example: convert 97.7°F

Example: convert 100.4°F

Example: convert 102.2°F

Why 98.6°F is not the only possible reading

The familiar 98.6°F or 37°C value is a commonly cited reference, not a rule that every person must show exactly that number at all times.

A recorded temperature can vary with:

• time of day;
• measurement location;
• thermometer type;
• recent activity;
• food or drink;
• environmental conditions;
• individual variation.

A converter expresses the same reading in another scale. It does not determine whether the reading is normal or concerning.

Measurement location can affect the reading

Oral, ear, forehead, rectal, and underarm measurements may not produce identical results. The difference is not caused by the Fahrenheit-to-Celsius conversion.

Record the measurement method along with the temperature when that context matters. Compare readings according to the instructions for the thermometer or the guidance of a qualified professional.

Thermometer precision and rounding

A digital thermometer may display tenths of a degree, while another device may use whole degrees or hundredths. The converted value should reflect the useful precision of the original reading.

Displaying many more digits than the thermometer measured can imply unsupported precision.

Keep the original reading in records

When possible, preserve the value and unit originally displayed by the thermometer. A record can show both units:

This helps avoid confusion caused by repeatedly converting rounded values back and forth.

Conversion does not provide medical interpretation

Converting a temperature does not diagnose an illness, identify the cause of symptoms, or determine treatment.

Follow the thermometer instructions and seek appropriate professional guidance when a medical decision depends on the reading, especially when symptoms are severe, persistent, or rapidly changing.

Common body-temperature conversion mistakes

Using the mental weather shortcut

Subtracting 30 and dividing by 2 is only an estimate and is not suitable for precise thermometer readings.

Rounding the Fahrenheit reading first

Convert 100.4°F directly instead of changing it to 100°F.

Comparing different measurement locations directly

Differences may result from the measurement method rather than the unit scale.

Using conversion as diagnosis

The conversion changes only the unit and does not interpret the result.

Dropping decimal digits

A difference of several tenths of a Fahrenheit degree can change the rounded Celsius result.

Related Fahrenheit to Celsius guides

Frequently asked questions