The formula
Celsius and Fahrenheit differ in two ways: where zero is, and how big a degree is. Water freezes at 0 °C = 32 °F and boils at 100 °C = 212 °F. Between freezing and boiling there are 100 degrees Celsius but 180 degrees Fahrenheit, so one degree Celsius equals 1.8 (9/5) degrees Fahrenheit.
°F = °C × 9/5 + 32
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°C = (°F − 32) × 5/9
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K = °C + 273.15
Kelvin is the scientific scale. It starts at absolute zero (−273.15 °C), the lowest possible temperature. A step of 1 kelvin is the same size as 1 degree Celsius, and kelvin is written without a degree sign: 300 K, not 300 °K.
Examples
- 37 °C to Fahrenheit: 37 × 9/5 + 32 = 66.6 + 32 = 98.6 °F, the classic body temperature.
- 180 °C to Fahrenheit (a European recipe): 180 × 9/5 + 32 = 356 °F, so set your oven to 350 °F.
- 100 °F to Celsius (a hot summer day): (100 − 32) × 5/9 ≈ 37.8 °C.
- −40 degrees: the only temperature that is the same on both scales: −40 °C = −40 °F.
A quick mental shortcut
For weather, this approximation is good enough:
- °C to °F: double it and add 30. 20 °C → 40 + 30 = 70 °F (exact: 68 °F).
- °F to °C: subtract 30 and halve it. 80 °F → 50 ÷ 2 = 25 °C (exact: 26.7 °C).
At oven temperatures the error gets too large, so use the exact formula or the calculator, which warns you when the shortcut is well off.
Chart of familiar temperatures
| °C | °F | What |
|---|---|---|
| −18 | 0 | freezer |
| 0 | 32 | water freezes |
| 4 | 39 | fridge |
| 20 | 68 | room temperature |
| 30 | 86 | hot summer day |
| 37 | 98.6 | normal body temperature |
| 38 | 100.4 | fever (from about 38 °C) |
| 100 | 212 | water boils at sea level |
| 180 | 356 | oven (cakes, casseroles) |
| 220 | 428 | oven (pizza, bread) |
Oven settings and gas marks
US recipes typically say 325, 350, 375 or 400 °F, which is about 160, 175, 190 and 200 °C. British recipes sometimes use gas marks: gas mark 4 is about 180 °C (350 °F). With a fan or convection oven, set the temperature 15–20 °C (about 25 °F) lower than the recipe says.
Who uses Fahrenheit?
The scale is named after Daniel Gabriel Fahrenheit, a German-born physicist who spent most of his working life in the Dutch Republic and published his scale in 1724. Today the United States and a handful of smaller countries and territories use Fahrenheit for weather and cooking. Almost everywhere else uses Celsius, named after the Swedish astronomer Anders Celsius. The UK uses Celsius officially, though older people and some newspapers still mention Fahrenheit in heatwaves. For other units, see the unit converter, cm to inches and kg to lbs.
Temperature when travelling and cooking
On a trip to Europe the weather forecast is in Celsius. A forecast of 10 °C sounds cold to American ears, and it is: about 50 °F, so bring a jacket. Around 21 °C (70 °F) is pleasant, and above 32 °C (90 °F) it is genuinely hot. Thermostats in European homes and hotels are typically set to about 20 °C (68 °F). In the kitchen the conversion matters most for baking, where a few degrees make a difference. Most meat thermometers can switch between °C and °F; the safe internal temperature for poultry, 165 °F, is about 74 °C.
Frequently asked questions
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 (or 1.8) and add 32. 25 °C × 1.8 + 32 = 77 °F.
How do I convert Fahrenheit to Celsius?
Subtract 32 and multiply by 5/9. (68 − 32) × 5/9 = 20 °C.
What is 350 °F in Celsius?
About 177 °C. Use 175–180 °C in a conventional oven or about 160 °C with a fan.
Is 100 °F a fever?
100 °F is 37.8 °C, a slightly raised temperature. A fever is usually defined as 100.4 °F (38 °C) or higher.
At what temperature are Celsius and Fahrenheit equal?
At −40: −40 °C is exactly −40 °F.
What is the difference between Celsius and Kelvin?
The steps are the same size, but Kelvin starts at absolute zero. Add 273.15 to a Celsius temperature to get kelvins.
Last reviewed: 2026-10-06. Results are estimates for information only.