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How to Convert Temperature Units
Published Apr 17, 2026
Three temperature scales are in common use:
- Celsius (°C) — the international standard for everyday use; water freezes at 0°C, boils at 100°C
- Fahrenheit (°F) — still used in the United States for weather, cooking, and body temperature
- Kelvin (K) — the SI base unit for thermodynamics; starts at absolute zero (no degree symbol)
Conversion Formulas
Celsius ↔ Fahrenheit
°F = (°C × 9/5) + 32
°C = (°F − 32) × 5/9
Example: 37°C (normal body temperature) → (37 × 9/5) + 32 = 66.6 + 32 = 98.6°F
Celsius ↔ Kelvin
K = °C + 273.15
°C = K − 273.15
Example: 0°C (freezing point) → 0 + 273.15 = 273.15 K
Fahrenheit ↔ Kelvin
K = (°F − 32) × 5/9 + 273.15
°F = (K − 273.15) × 9/5 + 32
Quick Reference Table
| Description | °C | °F | K |
|---|---|---|---|
| Absolute zero | −273.15 | −459.67 | 0 |
| Freezing point of water | 0 | 32 | 273.15 |
| Room temperature | 20–22 | 68–72 | 293–295 |
| Normal body temperature | 37 | 98.6 | 310.15 |
| Boiling point of water | 100 | 212 | 373.15 |
| Oven — moderate | 180 | 356 | 453 |
| Oven — hot | 220 | 428 | 493 |
Common Conversion Points to Memorise
A few anchor points make rough mental conversions easy:
- 0°C = 32°F (freezing)
- 20°C ≈ 68°F (mild room temp)
- 37°C = 98.6°F (body temp)
- 100°C = 212°F (boiling)
For a rough Celsius-to-Fahrenheit estimate: double the Celsius value and add 30. This gives ±2°F accuracy across 0–40°C.
Why Three Scales?
- Kelvin was defined for thermodynamic calculations where negative temperatures are meaningless. Gas laws (PV = nRT) use Kelvin.
- Celsius was designed so 0° and 100° align with water phase changes — intuitive for science and daily life.
- Fahrenheit was calibrated using brine (0°F) and body temperature (originally 96°F before revision). It remains in everyday use in the US.
Use the Temperature Converter to convert any value between all three scales instantly.