Temperature Converter
Celsius, Fahrenheit, Kelvin, Rankine — all at once.
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The Common Conversions
| From → To | Formula |
|---|---|
| Celsius → Fahrenheit | F = C × 9/5 + 32 |
| Fahrenheit → Celsius | C = (F − 32) × 5/9 |
| Celsius → Kelvin | K = C + 273.15 |
| Kelvin → Celsius | C = K − 273.15 |
| Fahrenheit → Rankine | R = F + 459.67 |
The Three Major Scales
- Celsius (°C) — 0 is water's freezing point, 100 is boiling. Used by ~95% of the world. Anders Celsius proposed the scale in 1742.
- Fahrenheit (°F) — 32 is freezing, 212 is boiling. Used in the U.S., Cayman Islands, Liberia, and parts of the Caribbean. Daniel Gabriel Fahrenheit proposed it in 1724.
- Kelvin (K) — Absolute zero is 0 K, water freezes at 273.15 K. Used in all scientific contexts. Defined since 2019 in terms of the Boltzmann constant.
The Wikipedia comparison page has every historical scale.
Useful Reference Points
| Phenomenon | °C | °F | K |
|---|---|---|---|
| Absolute zero | −273.15 | −459.67 | 0 |
| Dry ice sublimation | −78.5 | −109.3 | 194.65 |
| Water freezes | 0 | 32 | 273.15 |
| Refrigerator | 4 | 39 | 277 |
| Room temperature | 20-22 | 68-72 | 293-295 |
| Human body temp | 37.0 | 98.6 | 310.15 |
| Water boils (1 atm) | 100 | 212 | 373.15 |
| Pizza oven | 250-300 | 480-570 | 525-575 |
| Sun's surface | 5,500 | 9,930 | 5,775 |
Quick Mental Conversions
- Rough °C → °F: double C and add 30. A 20°C day ≈ 70°F (real: 68°F).
- Rough °F → °C: subtract 30 and halve. 80°F ≈ 25°C (real: 26.7°C).
- −40 trick: −40°C = −40°F exactly (the only point where both scales agree).