Converting temperatures trips people up because the scales don't line up the way length or weight units do. This converter handles Celsius, Fahrenheit and Kelvin, and explains why the maths is a little different.
Why temperature is special
Most unit conversions are a single multiplication because the units share a zero point. Temperature scales don't: 0°C and 0°F represent different temperatures, and Kelvin begins at absolute zero. So converting requires both a scaling factor and an offset — you can't just multiply.
The three formulas
Celsius to Fahrenheit: °F = °C × 9/5 + 32. Fahrenheit to Celsius: °C = (°F − 32) × 5/9. Celsius to Kelvin: K = °C + 273.15. Everything else is a combination of these.
Frequently asked questions
Multiply the Celsius value by 9/5 (or 1.8) and add 32. For example, 25°C × 1.8 + 32 = 77°F.
Subtract 32 from the Fahrenheit value, then multiply by 5/9. For example, (98.6 − 32) × 5/9 = 37°C.
Kelvin is the scientific temperature scale that starts at absolute zero (the coldest possible temperature). It uses the same step size as Celsius, so K = °C + 273.15.
At −40 degrees. −40°C equals exactly −40°F — the only point where the two scales meet.