Celsius to Kelvin Converter
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
Where the factor comes from
Since the 2019 revision, the kelvin is fixed by assigning the Boltzmann constant the exact value 1.380649 × 10⁻²³ J/K, tying temperature to energy rather than to the properties of any particular substance. The degree Celsius is then a derived unit with almost no independent content: it is defined by t/°C = T/K − 273.15, and that 273.15 is an exact conventional number, not a measurement. The degree interval is identical on both scales by construction, which is why this is a translation and never a scaling. One casualty of the redefinition is worth carrying: the triple point of water, formerly 273.16 K by definition, became an experimentally determined quantity with a small uncertainty attached. The Celsius offset stayed exact; the water fixed point did not.
Precision and significant figures
The offset is exact, so the arithmetic neither adds nor removes information and decimal places pass straight through. The trap is that 273.15 arrives with two decimals of its own and invites you to keep them. A bath read to the nearest degree is 25 °C, and writing 298.15 K claims five figures for a measurement supporting three — 298 K is the honest form. Real thermometry sets the ceiling anyway. A class A platinum resistance thermometer is specified near ±0.15 °C at the ice point and loosens as temperature rises; a base-metal thermocouple is doing well to hold ±2 °C. Neither earns the second decimal the constant hands over for free.
Worked Examples
Standard state for thermodynamic tables. Almost every ΔG° or ΔH° value you'll ever look up is reported at this temperature.
STP for gas-law calculations under the older convention. Water's freezing point, and the easiest mental conversion on this scale.
Water boiling at 1 atm. The Clausius–Clapeyron starting point you'll see in every physical chemistry course.
Liquid nitrogen boiling point. A useful number because it's the cryogen you'll actually pour into things.
Common mistakes
Rounding 273.15 down to 273
The 0.15 K discarded looks harmless near room temperature, and for a one-off gas-law calculation it is. It stops being harmless in an Arrhenius or van 't Hoff fit, where a constant shift applied to every T bends the line through ln k against 1/T and biases the activation energy that comes out of the slope. The extra digits cost nothing.
Writing °K or degrees Kelvin
The kelvin takes no degree sign — the symbol is a bare capital K, and the unit name is lowercase when spelled out. It also takes an ordinary plural in prose: 300 kelvins. The convention follows from the scale being absolute, with no arbitrary zero that a degree mark would distinguish. Journal copy editors still catch this one regularly.
Losing the minus sign on cold baths
A dry ice–acetone bath at −78 °C is 195.15 K. Enter the magnitude without its sign and you get 351.15 K, which is not an implausible number for a reaction and will not announce itself anywhere downstream. The 156 K gap turns a cryogenic step into a reflux. Sub-zero Celsius values deserve a second look before entering any absolute-scale expression.