Celsius to Fahrenheit converter

The formula

To turn Celsius into Fahrenheit, multiply by 9/5 (that is 1.8) and add 32. To go back, take away 32 and multiply by 5/9. These are the defined relations between the two scales, as given by NIST. The working line under the answer shows the sum with your number.

Worked example

20 °C × 9/5 = 36, and 36 + 32 = 68 °F. Going back, (68 − 32) × 5/9 = 36 × 5/9 = 20 °C. For a fever check, 38 °C is 100.4 °F.

A quick check in your head

Double the Celsius and add 30: 20 °C gives 70 °F, close to the true 68 °F. The shortcut drifts at the extremes, so use the exact answer for cooking and medicine.

Oven settings

Recipes often round oven temperatures: 180 °C is 356 °F, usually written as 350 °F, and 200 °C (392 °F) is written as 400 °F. Fan ovens are often set about 20 °C lower; follow the recipe.

Below zero

Use the Make negative / positive button if your phone keyboard has no minus key. −40 is the same in both scales. Nothing can be colder than absolute zero, −273.15 °C or −459.67 °F, so lower numbers get a message. Kelvin is shown as well; for all three scales see the temperature converter.

Rounding

The answer is worked out from the exact definition, then shown to 4 decimal places (6 significant figures for numbers below 1). It says "exactly" only when nothing was rounded.