Quick Answer: Celsius to Kelvin
0 °C equals 273.15 K, and 1 °C equals 274.15 K (K = °C + 273.15).
Conversely, 1 K = -272.15 °C.
Formula: K = °C + 273.15
Worked examples
- -273.15 °C = 0 K
- -100 °C = 173.15 K
- -40 °C = 233.15 K
Method and limitations
Add 273.15: K = °C + 273.15. The offset is exact by definition. Temperature differences convert 1:1, because one kelvin and one Celsius degree are the same size. Calculations use full-precision constants; answers in this box are rounded for readability (≈ marks a rounded value) and the calculator shows up to 9 significant figures. This converts a temperature reading (K = °C + 273.15). A temperature difference converts 1:1: a 1 °C interval is a 1 K interval. Kelvin is written K, not °K, and 0 K is absolute zero.
Each factor is exact by definition, derived from exact definitions, or a documented conventional value — see the methodology and sources.
Conversion Formula
Add 273.15: K = °C + 273.15. The offset is exact by definition. Temperature differences convert 1:1, because one kelvin and one Celsius degree are the same size.
Complete Guide to Celsius to Kelvin Conversion
What is the Celsius scale?
Celsius (°C) is defined from the kelvin as °C = K − 273.15, so it has the same degree size with a shifted zero.
What is the kelvin scale?
The kelvin (K) is the SI base unit of thermodynamic temperature. 0 K is absolute zero (−273.15 °C); negative kelvin readings do not occur.
How the Conversion Works
Only the zero point differs, so a reading is shifted by 273.15 and an interval is unchanged: 1 K interval = 1 °C interval.
Step-by-Step Conversion Guide
Follow these steps to convert celsius to kelvin manually:
Start with your value in celsius
Example: You want to convert -40 °C
Apply the conversion formula
Use the formula: K = °C + 273.15
Calculate the result
-40 °C = 233.15 K
Verify your answer
Use our calculator above to double-check your manual calculation.
Quick Mental Math Tip
Add 273 for a quick figure; keep the .15 whenever the result feeds a calculation.
Common Conversions
| Celsius (°C) | Kelvin (K) | Kelvin → Celsius |
|---|---|---|
| -273.15 °C | 0 | -273.15 K = -546.3 °C |
| -100 °C | 173.15 | -100 K = -373.15 °C |
| -40 °C | 233.15 | -40 K = -313.15 °C |
| 0 °C | 273.15 | 0 K = -273.15 °C |
| 20 °C | 293.15 | 20 K = -253.15 °C |
| 25 °C | 298.15 | 25 K = -248.15 °C |
| 37 °C | 310.15 | 37 K = -236.15 °C |
| 100 °C | 373.15 | 100 K = -173.15 °C |
| 500 °C | 773.15 | 500 K = 226.85 °C |
| 1000 °C | 1,273.15 | 1000 K = 726.85 °C |
Popular Celsius to Kelvin Conversions
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When You'll Need This Conversion
Formulas that need absolute temperature
Gas laws and radiation formulas require kelvin; a lab reading of 20 °C enters as 293.15 K.
Lighting colour temperature
Lamp colour temperatures are quoted in kelvin (for example 2700 K); they are not converted from a room temperature.
Common Mistakes to Avoid
Adding 273.15 to a difference
A 5 °C rise is a 5 K rise.
Offset readings only.
Writing °K
The degree sign was dropped from the kelvin in 1967.
Write 300 K.
Frequently Asked Questions
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Conversion factors on this page are either exact by definition, derived from exact definitions, or conventional values in documented use. Each is listed with its source in our conversion methodology and sources, which cites the BIPM SI Brochure, NIST Special Publication 811 and the relevant IEC or national standards. Results are rounded for display only; calculations use full precision.