The exact formula
°F = °C × 1.8 + 32. Multiply by 1.8 (or 9/5), then add 32. For example, 25 °C × 1.8 = 45, plus 32 is 77 °F.
Going the other way: °C = (°F − 32) ÷ 1.8. For example, (68 °F − 32) ÷ 1.8 = 20 °C.
A quick mental trick
Double the Celsius and add 30. 20 °C becomes 70 °F (exactly 68). It is within a few degrees for everyday weather, but drifts further off at oven and freezer temperatures. To go back, subtract 30 and halve.
Temperatures worth remembering
| Celsius | Fahrenheit |
| −40 °C | −40 °F (the two scales meet) |
| 0 °C | 32 °F (water freezes) |
| 20 °C | 68 °F (room temperature) |
| 37 °C | 98.6 °F (body temperature) |
| 100 °C | 212 °F (water boils at sea level) |
| 180 °C | 356 °F (a common oven setting, usually written 350 °F) |
Convert any value
The Temperature Converter converts Celsius, Fahrenheit and Kelvin instantly, in either direction.
How far off the quick trick is
| Celsius | Double and add 30 | Exact |
|---|---|---|
| −10 °C | 10 °F | 14 °F |
| 0 °C | 30 °F | 32 °F |
| 10 °C | 50 °F | 50 °F |
| 20 °C | 70 °F | 68 °F |
| 30 °C | 90 °F | 86 °F |
| 180 °C | 390 °F | 356 °F |
The trick is exact at 10 °C and gets worse the further you go from it, which is why it is fine for the weather and wrong for an oven.
A change in temperature is different
A rise of 10 °C is a rise of 18 °F, not 50 °F. For a difference between two temperatures, multiply by 1.8 and do not add 32: the 32 only moves the zero point. A fever 2 °C above normal is 3.6 °F above normal.