F to C Calculator

Common questions

What is the formula for Fahrenheit to Celsius?

C = (F − 32) × 5/9. The 32 comes off first, because 32 °F and 0 °C are the same temperature and that offset has to go before any scaling; then the multiply by 5/9 handles the size of the degree, since a Celsius degree is 9/5 as large as a Fahrenheit one. The reverse is F = C × 9/5 + 32, which the swap button between the two boxes does for you: 37 °C comes back as 98.6 °F and 100 °C as 212 °F.

What is 70 °F in Celsius?

21.1111111111 °C. A few more of the temperatures people look up: 50 °F is 10 °C, 60 °F is 15.5555555556 °C, 75 °F is 23.8888888889 °C, 80 °F is 26.6666666667 °C and 90 °F is 32.2222222222 °C. A whole number in Celsius only appears when F − 32 divides by 9, which is why 41 °F is exactly 5 °C and 68 °F exactly 20 °C while the values in between run to repeating decimals.

How do I convert F to C in my head?

Subtract 30 and halve what is left. 50 °F gives 10, which happens to be exact, and 70 °F gives 20 against a true 21.1111111111 °C. The shortcut reads about a degree low across the everyday range and drifts much further at the hot end: 212 °F gives 91 where the answer is 100. It is fine for a forecast, and the box above is there for the times the number matters.

Why is 98.6 °F exactly 37 °C?

Because 98.6 is the rounded conversion of 37, rather than the other way round. The 37 °C figure came first, from 19th-century measurement, and 37 × 9/5 + 32 is 98.6 with nothing left over, so the pair lines up to the decimal. Type either number here and the other comes back clean: 98.6 °F reads 37 °C, and swapping the units turns 37 °C back into 98.6 °F.

Where do Fahrenheit and Celsius meet?

At −40. Set the two scales equal in C = (F − 32) × 5/9 and −40 is the only solution, so −40 °F is −40 °C and nothing needs converting. It is also a quick test of whether a converter has its offset the right way round: a page that only multiplies will tell you 0 °F is 0 °C, and 0 °F is −17.7777777778 °C.

Is the decimal exact, or is it rounded?

The definition is exact; the decimal usually is not. Five ninths is a repeating fraction, so most Fahrenheit readings land on a repeating decimal: 0 °F is −17.777777... and the page shows −17.7777777778, twelve significant digits with the last one rounded. Values where F − 32 is a multiple of 9 come back exact instead: 32 °F is 0 °C, 41 °F is 5 °C, 68 °F is 20 °C, 104 °F is 40 °C and 212 °F is 100 °C.

What is 350 °F in Celsius for an oven?

176.666666667 °C, which is why recipes print 180 °C: an oven dial has no mark for the rest of it. 400 °F is 204.444444444 °C, usually written as 200, and 425 °F is 218.333333333 °C, usually written as 220. This page gives the arithmetic to the digit and leaves the rounding to a dial setting to you, since the direction you round matters more in a small oven than the decimals do.

Can I see Kelvin and Rankine as well?

Kelvin is already there. Under the answer the page lists the same temperature in every common unit of the category, so 98.6 °F shows as 37 °C and 310.15 K together, and each row has its own copy button. Rankine is marked as an uncommon unit, so it appears when you switch on Uncommon units in the readout strip, which adds the one extra row: 98.6 °F is 558.27 °R.

Will the page still open on Fahrenheit and Celsius if I last converted something else?

Yes. This page sets the pair on arrival, ahead of whatever the converter last remembered, and it leaves the main converter's own memory alone, so the full unit converter still opens on the pair you left it on. The number you last typed does travel with you, since it is usually the one you are still working on.