How to Convert Temperature Units

Formula

• °F = °C × 9/5 + 32
• °C = (°F − 32) × 5/9
• K = °C + 273.15
• °C = K − 273.15
• K = (°F + 459.67) × 5/9
• °F = K × 9/5 − 459.67

What the symbols mean:

• °C, °F, K: the temperature in degrees Celsius, degrees Fahrenheit and kelvins.
• 9/5 (1.8): how many Fahrenheit degrees make one Celsius degree. The other way, use 5/9.
• 32: the Fahrenheit value of 0 °C.
• 273.15: the kelvin value of 0 °C. The kelvin and the Celsius degree are the same size; the two scales are only shifted by this amount.
• 459.67: absolute zero on the Fahrenheit scale is −459.67 °F; this is that number without the sign.

The definitions come from the BIPM SI Brochure and NIST SP 811: t(°C) = T(K) − 273.15 and t(°F) = 1.8 × t(°C) + 32.

Step-by-step example

Convert an oven setting of 350 °F to Celsius:

1. Pick the formula: °C = (°F − 32) × 5/9.
2. Subtract 32 from the value: 350 − 32 = 318.
3. Multiply by 5/9: 318 × 5/9 ≈ 176.67.
4. The result: 350 °F ≈ 176.67 °C. The same temperature is (350 + 459.67) × 5/9 ≈ 449.82 K.

Common temperatures

The freezing and boiling points of water are approximate values at normal air pressure at sea level.

Common mistakes

• Converting a difference like a temperature. A temperature of 10 °C is 50 °F, but a rise of 10 °C is a rise of 18 °F. For a difference, do not add 32: a difference of 1 °C = 1 K = 1.8 °F. The temperature converter converts temperatures, not differences.
• Doing the steps in the wrong order. From Fahrenheit to Celsius, subtract 32 first and then multiply by 5/9. If you multiply first, the result is wrong.
• Writing a degree sign with kelvin. Write “300 K”, not “300 °K”.
• Entering a value below absolute zero. No temperature is lower than −273.15 °C, −459.67 °F or 0 K; the temperature converter rejects such values.