Degrees Fahrenheit to degrees Celsius converter

How to convert Fahrenheit to Celsius

Subtract 32 from the Fahrenheit temperature, then multiply by 5/9 (or divide by 1.8): °C = (°F − 32) × 5/9. For example, 98.6 °F − 32 = 66.6, and 66.6 × 5/9 = 37 °C. Always subtract first; for a temperature change, skip the 32 and just divide by 1.8.

Why subtract 32 first

Degrees Fahrenheit (°F) put water's freezing point at 32 and its sea-level boiling point at about 212, so the two are 180 degrees apart. Celsius, once called centigrade, covers that same range in 100 degrees, from 0 °C to 100 °C.

Subtracting 32 measures how far the reading sits above freezing. Multiplying by 100/180, which reduces to 5/9, rescales that distance into Celsius degrees, which count from freezing.

Fahrenheit to Celsius chart

Readings in the 30s are typical of fridges and winter mornings: 30 °F is just below freezing at −1.1 °C, while 35, 37 and 38 °F fall between 1.7 °C and 3.3 °C. −459.67 °F is absolute zero, the lowest reading possible.

Common Fahrenheit readings in Celsius

• Indoors: a thermostat at 68 °F is 20 °C, and 72 °F is 22.2 °C.
• Body temperature: the traditional normal of 98.6 °F is 37 °C, and 100.4 °F, the usual fever threshold, is 38 °C.
• Baking: 350 °F is 176.7 °C, 400 °F is 204.4 °C and 425 °F is 218.3 °C. Recipe tables round these to 180, 200 and 220 °C.
• Cold weather: 0 °F is −17.8 °C. Anything below 32 °F gives a negative Celsius number.

Why 98 °F gives 36.666… °C

Dividing by 9 rarely comes out even. 98 °F is exactly 110/3 °C, which never ends as a decimal: 36.666… °C. Round to the precision of the reading; a digital thermometer shows tenths, so 36.7 °C.

Writing the reading as 98.0 °F changes nothing in the arithmetic. The trailing zero only records how precisely it was measured.

Estimating in your head

Subtract 30 and halve: 70 °F becomes 20 °C, against an exact 21.1 °C. The estimate is exact at 50 °F (10 °C) and drifts by 0.5 °C for every 9 °F away from it.

That drift rules it out for ovens: 350 °F would give 160 °C instead of 176.7 °C. For fan ovens and gas marks, use the oven temperature converter.

Converting a temperature difference

A difference has no offset, so only divide by 1.8. A forecast that drops 18 °F overnight is a drop of 10 °C, and each 1 °F of change is 0.56 °C.

Subtracting 32 from that difference would turn the 18 °F drop into −7.8 °C, a reading below freezing, not a change. NIST gives separate factors for Fahrenheit readings and intervals.

Mistakes to avoid

• Multiplying before subtracting. 98.6 × 5/9 − 32 gives 22.8 instead of 37 °C.
• Using 9/5 instead of 5/9. (98.6 − 32) × 9/5 gives 119.9, more than the Fahrenheit reading. Above −40, the Celsius number is always the smaller one.
• Reading °F as °C. 37 °F is 2.8 °C, close to freezing; 37 °C is body temperature.

Other temperature scales

For the reverse step, use the Celsius to Fahrenheit converter. The Fahrenheit to Kelvin converter gives absolute temperature for gas-law problems, and the temperature converter adds Rankine and Réaumur.