Celsius to Kelvin Converter
Convert Celsius to Kelvin by adding 273.15. Includes a reference table from absolute zero to the surface of the Sun, and why kelvin has no degree sign and no negative values.
Celsius to Kelvin
Formula
Add 273.15. There is no multiplication — a kelvin and a Celsius degree are the same size.
That is why a temperature difference needs no conversion at all: a 5 °C rise is a 5 K rise. Only the starting point moves, and it moves to absolute zero — the coldest temperature physically possible.
Worked example
Convert a 25 °C laboratory:
And back from 300 K:
Conversion table
| Celsius (°C) | Kelvin (K) |
|---|---|
| -273.15 | 0 |
| -200 | 73.15 |
| -100 | 173.15 |
| -40 | 233.15 |
| 0 | 273.15 |
| 20 | 293.15 |
| 25 | 298.15 |
| 37 | 310.15 |
| 100 | 373.15 |
| 500 | 773.15 |
| 1,000 | 1,273.15 |
| 5,505 | 5,778.15 |
Reference temperatures
- Absolute zero — −273.15 °C = 0 K. Nothing can be colder.
- Liquid nitrogen boils — −195.8 °C = 77.35 K
- Dry ice sublimes — −78.5 °C = 194.65 K
- Water freezes — 0 °C = 273.15 K
- Standard lab conditions — 25 °C = 298.15 K
- Human body — 37 °C = 310.15 K
- Water boils — 100 °C = 373.15 K
- Incandescent filament — about 2,500 °C = 2,773 K
- Surface of the Sun — about 5,505 °C = 5,778 K
Why kelvin has no degree sign
Kelvin is an absolute scale, so its values are not degrees above an arbitrary reference — they are a direct measure of thermal energy from zero up. The unit is written "300 K", never "300 °K", and it is said as "three hundred kelvin", not "degrees kelvin". It is also the SI base unit for temperature, which is why physics formulas — the gas laws, Stefan–Boltzmann, Wien's law — all demand kelvin rather than Celsius.
Since the 2019 SI redefinition the kelvin is fixed through the Boltzmann constant at exactly 1.380649 × 10⁻²³ J/K, rather than through the triple point of water.
FAQ
What is 0 °C in kelvin? 273.15 K.
What is 0 K in Celsius? −273.15 °C, absolute zero.
Can kelvin be negative? Not for ordinary matter — 0 K is the floor. (Exotic "negative temperature" states exist in population-inverted systems, but they are hotter than any positive temperature, not colder.)
Do I need to convert a temperature change to kelvin? No. The degrees are the same size, so a change of 10 °C is a change of 10 K.
Why 273.15 and not 273? Because the scale was anchored so the triple point of water sits at exactly 273.16 K, which puts water's freezing point at 273.15 K. The extra 0.15 matters in precision work.