To convert Celsius to Kelvin, add 273.15. Formula: K = °C + 273.15. Examples: 0°C = 273.15 K, 25°C = 298.15 K, 100°C = 373.15 K. No multiplication needed - Celsius and Kelvin have identical degree sizes, only the zero point differs.
- Formula: K = °C + 273.15 (just a zero-point shift - no scaling factor).
- 0 K = −273.15°C - absolute zero, the lowest possible temperature.
- 25°C = 298.15 K - standard conditions in chemistry (STP uses 0°C; standard state uses 25°C).
- A change of 1 K equals a change of 1°C - the degree sizes are identical.
How to Use This Converter
Type any Celsius value in the °C field and the Kelvin result appears instantly. You can also type in the K field to convert back to Celsius - it works in both directions without pressing a button.
How Do You Convert Celsius to Kelvin?
Simply add 273.15. Unlike the Celsius–Fahrenheit conversion, there is no scaling factor because Kelvin and Celsius have the same degree size. The only difference is where zero sits: Kelvin's zero is absolute zero (the lowest possible temperature), while Celsius's zero is the freezing point of water.
$$K = °C + 273.15$$
Worked examples: 0°C = 273.15 K. 25°C = 298.15 K. 37°C = 310.15 K. 100°C = 373.15 K. −196°C = 77.15 K (liquid nitrogen). −273.15°C = 0 K (absolute zero).
Important: Kelvin uses no degree symbol. Write "298.15 K" not "298.15°K". Writing "degrees Kelvin" is technically incorrect because Kelvin is an absolute scale with a physically defined zero.
How Do You Convert Kelvin to Celsius?
Subtract 273.15. See the dedicated Kelvin to Celsius converter for a Kelvin-first reference table.
$$°C = K - 273.15$$
Worked examples: 0 K = −273.15°C. 273.15 K = 0°C. 298.15 K = 25°C. 373.15 K = 100°C.
Celsius to Kelvin Reference Table
Key scientific and physical fixed points converted using K = °C + 273.15:
| Celsius (°C) | Kelvin (K) | Context |
|---|---|---|
| −273.15°C | 0 K | Absolute zero |
| −196°C | 77.15 K | Liquid nitrogen boiling point |
| −78.5°C | 194.65 K | Dry ice (solid CO₂) sublimation |
| 0°C | 273.15 K | Water freezes (STP) |
| 20°C | 293.15 K | Room temperature |
| 25°C | 298.15 K | Standard state (chemistry) |
| 37°C | 310.15 K | Normal body temperature |
| 100°C | 373.15 K | Water boils at sea level |
| 1000°C | 1273.15 K | Approximate steel softening point |
When Do You Need to Convert Celsius to Kelvin?
Kelvin is the SI base unit of temperature and is required in all scientific calculations where the absolute temperature matters. Common use cases:
- Gas laws - the ideal gas law (PV = nRT) and related equations require absolute temperature in Kelvin. Using Celsius gives wrong results because 0°C is not zero energy.
- Thermodynamics - entropy, enthalpy, and Gibbs free energy calculations all require Kelvin.
- Chemistry - reaction rate equations (Arrhenius equation), equilibrium constants at standard state (298.15 K), and spectroscopy all use Kelvin.
- Astronomy and astrophysics - stellar temperatures and cosmic background radiation are stated in Kelvin.
- Cryogenics - working near absolute zero (superconductors, liquid helium at 4.2 K) requires Kelvin precision.
Frequently Asked Questions
How do you convert Celsius to Kelvin?
Add 273.15. Formula: K = °C + 273.15. Example: 25°C + 273.15 = 298.15 K. Unlike the Celsius-Fahrenheit conversion, there is no multiplication - just a simple addition because both scales use the same degree size.
What is 0°C in Kelvin?
0°C = 273.15 K. This is the freezing point of water at standard pressure. Absolute zero (0 K) is 273.15°C below this, at −273.15°C.
What is 25°C in Kelvin?
25°C = 298.15 K. This is the standard temperature for chemistry - thermodynamic data (ΔG°, ΔH°, S°) is tabulated at 298.15 K (25°C). STP (standard temperature and pressure) uses 273.15 K (0°C).
Why is Kelvin used in science instead of Celsius?
Because Kelvin is an absolute scale - 0 K is the absolute minimum temperature, not an arbitrary reference point. Many physical equations give nonsensical results if temperature can be zero or negative. Gas laws, thermodynamic efficiency calculations, and reaction rate equations all require an absolute temperature scale.