Temperature Converter — Celsius, Fahrenheit & Kelvin

How it works

The three everyday temperature scales differ in where they put zero and how big one degree is (NIST SP 811):

• Celsius (°C) sets 0 at water's freezing point and 100 at its boiling point.
• Fahrenheit (°F) sets those same points at 32 and 212, so a Fahrenheit degree is smaller — there are 180 of them between freezing and boiling versus 100 Celsius degrees.
• Kelvin (K) is the SI base unit. It uses the same degree size as Celsius but starts at absolute zero, the coldest possible temperature, which is −273.15 °C.

That gives the conversion relations:

°F = °C × 9/5 + 32 · K = °C + 273.15

Enter a value, choose the scale it is in, and choose the scale to convert to — the calculator applies the right relation (including the reverse and cross conversions, like Fahrenheit to Kelvin) for you.

Worked example

Converting 100 °C to Fahrenheit:

°F = 100 × 9/5 + 32 = 180 + 32 = 212 °F

And to Kelvin: 100 + 273.15 = 373.15 K. Going the other way, body temperature 98.6 °F is (98.6 − 32) × 5/9 = 37 °C.

Frequently asked questions

How do you convert Celsius to Fahrenheit?

Multiply the Celsius value by 9/5 (1.8) and add 32. For 100 °C that is 100 × 1.8 + 32 = 212 °F.

How do you convert Fahrenheit to Celsius?

Subtract 32, then multiply by 5/9. For 98.6 °F that is (98.6 − 32) × 5/9 = 37 °C.

How do you convert Celsius to Kelvin?

Add 273.15. Celsius and Kelvin use the same degree size, so only the zero point differs: 0 °C is 273.15 K, and 25 °C is 298.15 K.

What is absolute zero?

Absolute zero is the lowest possible temperature, where thermal motion is minimal. It is 0 K, which equals −273.15 °C or −459.67 °F.

Why is a Fahrenheit degree smaller than a Celsius degree?

Because Fahrenheit spreads 180 degrees between water's freezing (32 °F) and boiling (212 °F) points, while Celsius spreads only 100 between 0 and 100. So one Celsius degree equals 1.8 Fahrenheit degrees.

At what temperature are Celsius and Fahrenheit equal?

At −40°: −40 °C is exactly −40 °F. It is the one point where the two scales cross.