How do I convert Celsius to Fahrenheit?

Multiply the Celsius temperature by 1.8 and add 32. For 25 °C: 25 × 1.8 = 45, plus 32 is 77 °F.

How do I convert Fahrenheit to Celsius?

Subtract 32, then divide by 1.8. For 68 °F: 68 − 32 = 36, and 36 ÷ 1.8 = 20 °C.

At what temperature are Celsius and Fahrenheit equal?

At −40. Both scales read −40 at that temperature.

Why does Kelvin not use the degree symbol?

Kelvin is an absolute scale measured in its own unit, so it is written as 300 K, not 300 °K.

Temperature Converter: Celsius, Fahrenheit and Kelvin

To convert Celsius to Fahrenheit, multiply by 9/5 (1.8) and add 32: 20 °C is 68 °F. To convert Fahrenheit to Celsius, subtract 32 and multiply by 5/9.

Temperature

°C

Celsius
20.00 °C
Fahrenheit
68.00 °F
Kelvin
293.15 K

Quick check: °F = °C × 1.8 + 32. The dashed line marks freezing (0 °C). Thermometer shows −50 to 50 °C.

Show the math

1
Celsius to Fahrenheit
20 × 9 ÷ 5 + 32 = 68
Multiply by 9/5 (1.8), then add 32, because the two scales start at different points.
= 68 °F

Read the steps as text

Celsius to Fahrenheit. 20 × 9 ÷ 5 + 32 = 68 Multiply by 9/5 (1.8), then add 32, because the two scales start at different points.
Celsius to Kelvin. 20 + 273.15 = 293.15 Kelvin uses the same size of degree as Celsius but starts at absolute zero.

The conversion formulas

Celsius to Fahrenheit: °F = °C × 9/5 + 32. Fahrenheit to Celsius: °C = (°F − 32) × 5/9. Celsius to Kelvin: K = °C + 273.15. Kelvin to Celsius: °C = K − 273.15. The Show the math panel works through the version you need with your own numbers.

The scales differ in two ways. A Fahrenheit degree is smaller than a Celsius degree (there are 180 Fahrenheit degrees between freezing and boiling water, but only 100 Celsius degrees), and they start at different zero points. That is why the formulas both scale by 9/5 and shift by 32.

Handy reference temperatures

Water freezes at 0 °C (32 °F) and boils at 100 °C (212 °F) at sea level. A comfortable room is about 20 to 22 °C (68 to 72 °F). Normal body temperature is about 37 °C (98.6 °F). The two scales meet at −40, where −40 °C equals −40 °F.

Kelvin is the scientific scale. It uses the same size of degree as Celsius but starts at absolute zero (−273.15 °C), the coldest temperature possible, so it has no negative values. Kelvin temperatures are written without a degree symbol.

Mental shortcuts

For a quick estimate from Celsius to Fahrenheit, double the number and add 30: 20 °C becomes about 70 °F, close to the exact 68 °F. In the other direction, subtract 30 and halve it. The shortcut drifts at extreme temperatures, so use the calculator when accuracy matters, such as for cooking, science or travel forecasts.

Frequently asked questions

How do I convert Celsius to Fahrenheit?: Multiply the Celsius temperature by 1.8 and add 32. For 25 °C: 25 × 1.8 = 45, plus 32 is 77 °F.
How do I convert Fahrenheit to Celsius?: Subtract 32, then divide by 1.8. For 68 °F: 68 − 32 = 36, and 36 ÷ 1.8 = 20 °C.
At what temperature are Celsius and Fahrenheit equal?: At −40. Both scales read −40 at that temperature.
Why does Kelvin not use the degree symbol?: Kelvin is an absolute scale measured in its own unit, so it is written as 300 K, not 300 °K.