Most conversions are a simple multiplication. Temperature is the interesting exception: because each scale starts counting from a different zero point, converting between them requires both a multiplier and an offset.
The four scales
- Celsius (°C) puts 0° at the freezing point of water and 100° at its boiling point (at standard pressure). It’s the everyday scale for most of the world.
- Fahrenheit (°F) puts water’s freezing point at 32° and boiling at 212°. It’s standard for daily use in the United States.
- Kelvin (K) starts at absolute zero — the coldest possible temperature — and uses the same step size as Celsius. It’s the SI unit and is used throughout science.
- Rankine (°R) starts at absolute zero but uses the Fahrenheit-sized degree.
The exact formulas
- Celsius to Fahrenheit: °F = °C × 1.8 + 32
- Fahrenheit to Celsius: °C = (°F − 32) ÷ 1.8
- Celsius to Kelvin: K = °C + 273.15
- Kelvin to Celsius: °C = K − 273.15
Try them live with the Celsius to Fahrenheit converter or the Fahrenheit to Celsius converter.
Why the offset matters
Because the scales don’t share a zero, you cannot simply scale a temperature the way you scale a length. Doubling 10 °C does not give you the same physical change as doubling 50 °F. This is why Units Verse models temperature as an affine relationship (multiply, then add), which reproduces the classic formulas exactly — see our methodology.
Handy reference points
| Description | °C | °F | K |
|---|---|---|---|
| Absolute zero | −273.15 | −459.67 | 0 |
| Water freezes | 0 | 32 | 273.15 |
| Room temperature | 20 | 68 | 293.15 |
| Body temperature | 37 | 98.6 | 310.15 |
| Water boils | 100 | 212 | 373.15 |
A quick mental trick
To go from Celsius to Fahrenheit fast: double the Celsius value and add 30. It’s not exact (the real factor is 1.8, not 2), but it gets you within a few degrees — enough to decide whether to bring a jacket.