How to Convert Celsius to Kelvin
Converting Celsius to Kelvin is one of the most common temperature conversions in physics and chemistry. The good news: it's the simplest temperature formula you'll ever use.
The Formula
K = °C + 273.15
That's it. Just add 273.15 to any Celsius temperature to get Kelvin. No multiplication required.
Why 273.15?
Absolute zero — the coldest theoretically possible temperature — is −273.15°C. Since the Kelvin scale starts at absolute zero, we simply shift the Celsius scale up by 273.15 units. At 0 Kelvin, all molecular motion stops.
Worked Examples
| Celsius (°C) | Kelvin (K) | What it represents |
|---|---|---|
| −273.15°C | 0 K | Absolute zero |
| 0°C | 273.15 K | Freezing point of water |
| 20°C | 293.15 K | Room temperature |
| 37°C | 310.15 K | Human body temperature |
| 100°C | 373.15 K | Boiling point of water |
| −40°C | 233.15 K | Extreme cold weather |
When is Kelvin Used?
- Physics: Gas laws (PV = nRT uses Kelvin), thermodynamics equations
- Chemistry: Reaction rates, Boltzmann constant calculations
- Astronomy: Star surface temperatures, cosmic microwave background
- Engineering: Cryogenics, semiconductor physics
💡 Quick tip: When your physics or chemistry formula uses temperature (T), always convert to Kelvin first. Using Celsius in those formulas gives wrong answers.
Converting Back: Kelvin to Celsius
Simply reverse the formula: °C = K − 273.15
For example: 373 K − 273.15 = 99.85°C ≈ 100°C (boiling point of water).