Temperature Converter
Convert between Celsius, Fahrenheit and Kelvin instantly.
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Reference Points
Water freezes
0°C / 32°F
Room temperature
21°C / 70°F
Average body temperature
37°C / 99°F
Water boils
100°C / 212°F
How this temperature converter works
Every conversion routes through Celsius as a common reference point — Fahrenheit and Kelvin values are first converted to Celsius, then from Celsius to the target scale — which is why Celsius-to-Celsius is always an exact 1:1 pass-through.
Fahrenheit uses (°C × 9/5) + 32, while Kelvin is simply Celsius plus 273.15 — Kelvin has no negative values since 0 K represents absolute zero, the coldest physically possible temperature.
Common reference points
Water freezes at 0°C / 32°F / 273.15K and boils at 100°C / 212°F / 373.15K (at sea level). Average human body temperature is about 37°C / 98.6°F. Room temperature is commonly cited as roughly 20-22°C / 68-72°F. These fixed points are a quick way to sanity-check any conversion this calculator gives you.
Where the three scales come from
Fahrenheit, proposed by Daniel Gabriel Fahrenheit in 1724, was originally based on a brine solution's freezing point as zero. Celsius, introduced by Anders Celsius in 1742, set 0 and 100 at water's freezing and boiling points for a cleaner decimal scale. Kelvin, developed by William Thomson (Lord Kelvin) in 1848, uses the same size degree as Celsius but starts at absolute zero, making it the scale of choice for scientific work where negative temperatures would be physically meaningless.
A quick mental-math trick
For a rough Celsius-to-Fahrenheit estimate without a calculator, double the Celsius value and add 30 — 20°C × 2 + 30 = 70°F, close to the exact 68°F. It's not precise (the real multiplier is 1.8, not 2), but it's a handy sanity check for gut-checking whether a converted number looks roughly right.
Frequently Asked Questions
What's the formula to convert Celsius to Fahrenheit?
°F = (°C × 9/5) + 32. To go the other way, °C = (°F − 32) × 5/9. This calculator also supports Kelvin for scientific use.
What is 0°C in Fahrenheit?
0°C equals 32°F — the freezing point of water on both scales, just expressed with different zero points and interval sizes.
What is normal human body temperature in Celsius and Fahrenheit?
Roughly 37°C (98.6°F), though normal individual variation of half a degree or so in either direction is common and not necessarily a sign of illness.
Why doesn't Kelvin have negative values?
0 Kelvin represents absolute zero, the coldest physically possible temperature — there's nothing colder to represent with a negative number. Kelvin uses the same size degree as Celsius, just starting from that absolute floor instead of water's freezing point.
Is there a quick mental-math trick for Celsius to Fahrenheit?
Double the Celsius value and add 30 for a rough estimate — 20°C × 2 + 30 = 70°F, close to the exact 68°F. It's not precise (the real multiplier is 1.8, not 2), but it's handy for a fast sanity check.