Fahrenheit to Celsius

Formula: °C = (°F − 32) × 5/9

Fahrenheit to Celsius chart

Related: Celsius to Fahrenheit · kg to lbs · cm to inches · km to miles

Fahrenheit to Celsius at a glance

Fahrenheit is used day to day in the United States. The 98.6 row is normal body temperature; 32 and 212 are water freezing and boiling.

Why temperature needs an offset

Most unit conversions are a single multiplication, because both scales start at the same zero. Temperature does not: 0 °C and 0 °F are different temperatures, so the conversion needs a shift as well as a scale factor.

°F = (°C × 9/5) + 32
°C = (°F − 32) × 5/9

Forgetting the 32 is the usual error, and it is easy to miss because the result still looks plausible. Two anchors worth memorising: 0 °C = 32 °F (water freezes) and100 °C = 212 °F (water boils). The scales also cross at −40, where both readings are the same number.

For a rough figure in your head, doubling and adding 30 gets close for everyday temperatures — 20 °C estimates to 70 °F against an actual 68 °F. Use the exact formula whenever the number matters.

Rounding, and how precise to be

Converting does not create accuracy that was not in the original measurement. If someone tells you a distance in whole fahrenheit, the converted figure is only as good as that starting estimate — quoting it to four decimal places implies a precision nobody measured.

A practical rule: keep roughly the same number of significant figures you started with, and round only at the end. Rounding at each intermediate step compounds the error, which is how a chain of conversions drifts away from the right answer.

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