Everyday guide
How to Convert Celsius to Fahrenheit (and Back)
Updated 28 September 2026 · 3 min read
Most of the world uses Celsius; the United States uses Fahrenheit. Converting between them takes one formula each way — and there's a shortcut you can do in your head. For an exact answer, use the Celsius to Fahrenheit or Fahrenheit to Celsius converter.
Open the free Celsius to FahrenheitThe formulas
- Celsius to Fahrenheit: °F = °C × 9/5 + 32 (or × 1.8 + 32)
- Fahrenheit to Celsius: °C = (°F − 32) × 5/9 (or ÷ 1.8)
Example: 25 °C × 1.8 = 45, + 32 = 77 °F. And back: 77 − 32 = 45, ÷ 1.8 = 25 °C.
A quick way to do it in your head
°C to °F: double it and add 30. 20 °C → 40 + 30 = 70 °F (exact: 68 °F). °F to °C: take away 30 and halve it. 80 °F → 50 ÷ 2 = 25 °C (exact: 26.7 °C). It's within a few degrees across everyday weather — good for deciding what to wear, not for cooking or medicine.
An exact method you can still do in your head
For an exact answer without a calculator: °C to °F — double it, take off a tenth of that, then add 32. 20 °C → 40 − 4 = 36, + 32 = 68 °F. °F to °C — take off 32, halve it, then add a ninth of the result. 68 °F → 36 ÷ 2 = 18, + 2 = 20 °C. It's the same as multiplying or dividing by 1.8, just easier to do mentally.
Common temperatures
| °C | °F | What it is |
|---|---|---|
| −40 | −40 | The one temperature that's the same on both scales |
| −18 | 0 | A typical freezer |
| 0 | 32 | Water freezes |
| 10 | 50 | A cool day |
| 20 | 68 | Room temperature |
| 30 | 86 | A hot day |
| 37 | 98.6 | Normal body temperature |
| 38 | 100.4 | Commonly used as the threshold for a fever |
| 100 | 212 | Water boils (at sea level) |
Oven temperatures
Recipes round oven temperatures to convenient numbers, so conversions aren't exact:
| °C | °F (exact) | °F (as in recipes) |
|---|---|---|
| 150 | 302 | 300 |
| 160 | 320 | 325 |
| 180 | 356 | 350 |
| 200 | 392 | 400 |
| 220 | 428 | 425 |
Converting a temperature change
A difference in temperature converts without the 32. A rise of 10 °C is a rise of 18 °F (10 × 1.8), not 50 °F. This matters when reading climate figures or a recipe that says "lower the heat by 20 degrees".
Body temperature isn't one number
37 °C (98.6 °F) is an average. Healthy body temperature varies from person to person, through the day and with where it's measured — an ear or rectal reading is usually a little higher than one taken under the arm. For concerns about a fever, especially in babies, follow your doctor's or local health service's advice.
Who uses Fahrenheit?
The United States is by far the largest country that uses Fahrenheit for everyday temperatures, along with a few smaller countries and territories. Almost everywhere else — and science worldwide — uses Celsius, which is why travellers, students and anyone following an American recipe end up converting.
What about Kelvin?
Scientists use Kelvin, which starts at absolute zero: K = °C + 273.15. So 20 °C is 293.15 K. The Temperature Converter converts between Celsius, Fahrenheit, Kelvin and Rankine.