Temperature Conversion
Quick answer: °F = °C × 9/5 + 32, °C = (°F − 32) × 5/9 and K = °C + 273.15. Examples: 0 °C = 32 °F = 273.15 K, 20 °C = 68 °F, −40 °C = −40 °F.
Degrees Celsius, Fahrenheit, kelvin, Rankine and Réaumur – exact conversion with the scale offset, including negative temperatures.
How the calculation works
Enter a temperature (it may be negative) and choose the scale. The table shows the same temperature in °C, K, °F, °R and °Ré. Values below absolute zero (0 K = −273.15 °C) are not shown.
Formula and assumptions
Temperature scales have different zero points, so they are converted with an offset as well as a factor: K = °C + 273.15; °F = °C × 1.8 + 32; °R = K × 1.8; °Ré = °C × 0.8. For a temperature difference (for example ΔT in a U-value) only the factor applies: 1 K = 1 °C = 1.8 °F.
More worked examples
- Room temperature 20 °C: 20 × 1.8 + 32 = 68 °F.
- A US summer day of 95 °F: (95 − 32) × 5/9 = 35 °C.
- Boiling water 100 °C = 373.15 K = 212 °F.
- Winter −10 °C = 14 °F = 263.15 K.
Scale comparison
| °C | °F | K |
|---|---|---|
| −40 | −40 | 233.15 |
| −18 | −0.4 | 255.15 |
| 0 | 32 | 273.15 |
| 20 | 68 | 293.15 |
| 37 | 98.6 | 310.15 |
| 100 | 212 | 373.15 |
Common mistakes
- Multiplying by 1.8 without adding 32.
- Mixing a temperature and a temperature difference: a 10 °C difference is 18 °F, not 50 °F.
- Writing “°K” – the kelvin has no degree sign (K).
Frequently asked questions
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 (1.8) and add 32: 25 °C × 1.8 + 32 = 77 °F.
How do I convert Fahrenheit to Celsius?
Subtract 32 and multiply by 5/9: (50 °F − 32) × 5/9 = 10 °C.
At what temperature are °C and °F equal?
At −40: −40 °C = −40 °F.
How many kelvin is 0 °C?
0 °C = 273.15 K. Absolute zero is 0 K = −273.15 °C = −459.67 °F.
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