Temperature Converter
Convert temperature between Celsius, Fahrenheit and Kelvin with exact formulas, common reference points and a quick conversion table.
The exact formulas
Temperature scales differ in both step size and zero point, so — unlike length or weight — conversion needs a
formula rather than a single multiplier:
- °F = °C × 9/5 + 32 · °C = (°F − 32) × 5/9
- K = °C + 273.15 · °C = K − 273.15
- °F = (K − 273.15) × 9/5 + 32
Celsius anchors 0° and 100° to water’s freezing and boiling points. Fahrenheit places them at 32° and 212° —
180 Fahrenheit degrees for every 100 Celsius degrees, hence the 9/5 ratio. Kelvin keeps Celsius-sized degrees
but starts counting from absolute zero (−273.15 °C), which is why science uses it: no negative values.
Reference points
Common Celsius to Fahrenheit reference temperatures | °C | °F | What it feels like |
|---|
| −40 | −40 | The point where both scales meet |
| 0 | 32 | Water freezes |
| 25 | 77 | Warm room / pleasant day |
| 37 | 98.6 | Normal body temperature |
| 100 | 212 | Water boils (at sea level) |
Handy mental shortcuts
- °C → °F roughly: double it and add 30 (25 °C → ~80 °F; exact is 77 °F)
- °F → °C roughly: subtract 30 and halve (70 °F → ~20 °C; exact is 21.1 °C)
- 16 °C = 61 °F and 28 °C = 82 °F — the digits swap, a handy pair to memorise
Frequently asked questions
What is 25 °C in Fahrenheit?
25 °C = 77 °F. Use °F = °C × 9/5 + 32: 25 × 1.8 = 45, plus 32 gives 77 — a warm, pleasant day.
How do I convert Fahrenheit to Celsius?
Subtract 32, then multiply by 5/9: °C = (°F − 32) × 5/9. So 98.6 °F → 66.6 × 5/9 = 37 °C, and 68 °F is exactly 20 °C.
At what temperature are Celsius and Fahrenheit equal?
At −40 degrees: −40 °C = −40 °F. Solving C = 1.8C + 32 gives C = −40 — the only point where the two scales read the same number.
What is 0 Kelvin?
0 K is absolute zero, −273.15 °C (−459.67 °F) — the lowest possible temperature, where molecular motion is at its minimum. Kelvin uses Celsius-sized degrees but starts at absolute zero, so K = °C + 273.15 and there are no negative kelvins.
Is 40 °C a fever?
Yes — 40 °C is 104 °F, a high fever. Normal body temperature is about 37 °C (98.6 °F), and anything above roughly 38 °C (100.4 °F) counts as a fever.