100°F to Celsius

37.8°C

100°F = 37.8°C = 310.93 K

Working: (100 − 32) × 5/9 = 37.8

100 degrees Fahrenheit converts to 37.8 degrees Celsius. A reading of 100°F is a fever in adults; medical guidance generally treats 100.4°F (38°C) and above as a fever.

To convert Fahrenheit to Celsius, subtract 32 first, then multiply by 5/9. For 100°F: 100 − 32 = 68, and 68 × 5/9 = 37.8. The subtraction comes first because the two scales have different zero points — water freezes at 0°C but at 32°F.

A quick mental estimate is to subtract 30 and halve the result, which gives about 35°C — 2.8 degrees off the exact 37.8°C. That is close enough to judge the weather, though it drifts badly at oven temperatures.

One hundred Fahrenheit is a round number in one scale and 37.8°C in the other — just above normal body temperature but below the usual clinical threshold for fever, which is set at 100.4°F, or exactly 38°C. That 0.4 gap is why the American threshold looks so oddly specific: it is a converted metric round number.

Nearby temperatures

Fahrenheit	Celsius
68°F	20°C
72°F	22.2°C
80°F	26.7°C
90°F	32.2°C
98°F	36.7°C
101°F	38.3°C
103°F	39.4°C
105°F	40.6°C

Try another value

From

°C

77°F

All scales

Celsius (°C)25 °C

Fahrenheit (°F)77 °F

Kelvin (K)298.15 K

Frequently asked questions

What is 100 degrees Fahrenheit in Celsius?

100°F is 37.8°C. Subtract 32 from 100 to get 68, then multiply by 5/9 to get 37.8.

What is the formula for Fahrenheit to Celsius?

°C = (°F − 32) × 5/9. Subtract 32 from the Fahrenheit temperature, then multiply the result by 5/9 (about 0.5556).

For any other value, use the full Temperature Converter on BrainVert.