Temperature converter
Convert between Celsius, Fahrenheit and Kelvin.
How the calculation works
Unlike meters or kilos, temperature isn't converted by a single factor — the scales have different starting points (zeros). So each conversion has its own formula.
Celsius ⇄ Fahrenheit
°F = °C × 9/5 + 32
°C = (°F − 32) × 5/9
The "× 9/5" adjusts the degree size (a Fahrenheit degree is smaller) and "+ 32" fixes the freezing point, which is 0 °C but 32 °F.
Celsius ⇄ Kelvin
K = °C + 273.15
Kelvin uses the same degree size as Celsius but starts at absolute zero (−273.15 °C), the lowest possible temperature. So Kelvin is never negative.
Step by step: 25 °C to Fahrenheit
- 25 × 9/5 = 45
- 45 + 32 = 77 °F
Handy reference points
| °C | °F | K | |
|---|---|---|---|
| Water freezes | 0 | 32 | 273.15 |
| Room temperature | 25 | 77 | 298.15 |
| Human body | 37 | 98.6 | 310.15 |
| Water boils | 100 | 212 | 373.15 |
Fun fact: −40 °C and −40 °F are exactly the same temperature — the only point where both scales meet.
Examples
- 30 °C to °F: 30 × 9/5 + 32 = 86 °F.
- 98.6 °F to °C: (98.6 − 32) × 5/9 = 37 °C.
- 0 °C to Kelvin: 0 + 273.15 = 273.15 K.
Frequently asked questions
Why does the formula add 32?
Because Celsius and Fahrenheit have different zeros: water freezes at 0 °C but 32 °F. The "+ 32" aligns that starting point.
Can Kelvin be negative?
No. Kelvin starts at absolute zero (−273.15 °C), the lowest possible temperature, so it is never negative.
At what point are Celsius and Fahrenheit equal?
−40 degrees: −40 °C = −40 °F. The only value where both scales coincide.
Any quick mental conversion?
From °C to °F: double and add 30 (rough). 20 °C → 40 + 30 = 70 °F (exact is 68). Good enough for daily use.
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Updated on June 17, 2026 · by Rafael Rossi · Methodology & sources