Temperature Converter
Convert Celsius, Fahrenheit, and Kelvin.
Conversion sheet
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Temperature is the one common conversion that isn't a simple multiplication. Because Celsius, Fahrenheit, and Kelvin start their scales at different points, you have to shift and scale — which is exactly why a quick 'times two' rule never quite works.
How it works
Temperature uses offset formulas, not simple factors: °C = (°F − 32) × 5/9, K = °C + 273.15.
Unlike length or weight, temperature scales have different zero points, so each conversion uses an offset formula rather than a single factor. Celsius and Kelvin share the same step size (1 degree), but Kelvin's zero is absolute zero, 273.15 degrees below the freezing point of water.
Fahrenheit uses both a different zero and a different step size: each Fahrenheit degree is only 5/9 of a Celsius degree. That 5/9 factor, combined with the 32-degree offset, is the source of most hand-calculation mistakes.
°C = (°F − 32) × 5/9; °F = (°C × 9/5) + 32; K = °C + 273.15.
Worked examples
Convert 72°F (a comfortable room) to Celsius. → 22.22°C
(72 − 32) × 5/9 = 40 × 0.5556 = 22.22°C.
Convert 100°C (boiling water) to Fahrenheit and Kelvin. → 212°F / 373.15 K
(100 × 9/5) + 32 = 212°F; 100 + 273.15 = 373.15 K.
Tips & gotchas
- Two reference points anchor everything: water freezes at 0°C / 32°F and boils at 100°C / 212°F. If your answer falls outside that span unexpectedly, recheck the direction.
- For a rough Fahrenheit-to-Celsius estimate, subtract 30 and halve: 72 → 42 ÷ 2 = 21, close to the exact 22.2.
- Never add 273.15 to Fahrenheit. Kelvin is built on the Celsius scale, so always convert to Celsius first, then to Kelvin.
- −40 is the single point where Celsius and Fahrenheit read the same number — a handy sanity check that your formula is wired correctly.
FAQ
Why can't I just multiply Fahrenheit by a single factor?
Because the scales don't share a zero. Fahrenheit's zero is not Celsius's zero, so any conversion needs both a multiply (5/9 or 9/5) and an add or subtract (the 32-degree shift).
What is absolute zero in each scale?
Absolute zero is 0 K, which equals −273.15°C and −459.67°F. Nothing can be colder, and no negative Kelvin values exist.
Is there a temperature that reads the same in Celsius and Fahrenheit?
Yes, −40°. At that point −40°C and −40°F are identical, which is the only number where the two scales cross.
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