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Celsius to Kelvin Converter
↔ Convert K to °C instead

Common Conversions

°C K
-273.15 0
-196 77.15
-78 195.15
-40 233.15
0 273.15
20 293.15
25 298.15
37 310.15
100 373.15
200 473.15
500 773.15
1000 1273.15

Why this conversion matters in chemistry

Kelvin is what the equations want. PV = nRT, the Arrhenius expression, every equilibrium constant — all of them need absolute temperature, and that means Celsius plus 273.15. Skip the step and strange things happen: a rate constant plotted against 1/T where T is in Celsius won't be linear, a van't Hoff analysis will give you a fit that looks convincing and is wrong, an ideal gas calculation at room temperature will come back off by more than an order of magnitude because 25 is so much smaller than 298. The conversion is trivial arithmetic, but it's the kind of step you really don't want to forget. The safest habit is to convert the moment you read a temperature off a thermometer, before anything else touches the number.

Formula

K = °C + 273.15

Worked Examples

25°C = 298.15 K

Standard state for thermodynamic tables. Almost every ΔG° or ΔH° value you'll ever look up is reported at this temperature.

0°C = 273.15 K

STP for gas-law calculations under the older convention. Water's freezing point, and the easiest mental conversion on this scale.

100°C = 373.15 K

Water boiling at 1 atm. The Clausius–Clapeyron starting point you'll see in every physical chemistry course.

-196°C = 77.15 K

Liquid nitrogen boiling point. A useful number because it's the cryogen you'll actually pour into things.

Frequently Asked Questions

Why do chemistry calculations insist on Kelvin?
Because the equations were built around an absolute scale. In PV = nRT, T is the absolute temperature — if you double T, you double the right-hand side. That only works if T starts at absolute zero, which Celsius doesn't. Drop Celsius into the ideal gas law at room temperature and you're off by roughly an order of magnitude; the whole proportionality falls apart.
How do you convert Celsius to Kelvin?
Add 273.15. So 25°C becomes 298.15 K, and 100°C becomes 373.15 K. Kelvin doesn't take a degree symbol — it's just K, no °. A small convention, but the kind of thing journal editors still notice.
What's standard temperature in Kelvin?
Thermodynamic standard state is 298.15 K (25°C); STP for gas calculations is usually 273.15 K (0°C). IUPAC changed STP pressure to 1 bar instead of 1 atm back in 1982, which is a footnote worth knowing when comparing older and newer tables.
Can Kelvin be negative?
Not in any ordinary thermodynamic sense. Kelvin starts at 0 — absolute zero — and there's nothing colder. (There's a technical subculture around "negative absolute temperature" in specialized systems with bounded energy states, but it's not something that ever turns up in a chemistry calculation you'd do with a calculator.)