The formulas
Celsius → Fahrenheit: °F = (°C × 9/5) + 32
Fahrenheit → Celsius: °C = (°F − 32) × 5/9
Example: 20°C → (20 × 9/5) + 32 = 36 + 32 = 68°F (pleasant room temperature). Reverse: 68°F → (68 − 32) × 5/9 = 36 × 5/9 = 20°C. The formulas are exact inverses — round-trip conversion returns your starting value.
For instant results without arithmetic, our unit converter handles temperature both ways with a tap-to-swap button.
Reference table
| Celsius | Fahrenheit | What it feels like |
|---|---|---|
| −40°C | −40°F | The crossover point — both scales agree |
| −18°C | 0°F | A harsh winter day |
| 0°C | 32°F | Water freezes |
| 10°C | 50°F | Cool jacket weather |
| 20°C | 68°F | Comfortable room temperature |
| 25°C | 77°F | Warm summer day |
| 30°C | 86°F | Hot day |
| 37°C | 98.6°F | Human body temperature |
| 100°C | 212°F | Water boils (sea level) |
Mental-math shortcuts
- C → F, quick estimate: double the Celsius and add 30. (20°C → ~70°F; actual 68°F. Good within a few degrees.)
- F → C, quick estimate: subtract 30, then halve. (70°F → ~20°C; actual 21.1°C.)
- Memorize anchors: 0°C=32°F, 10°C=50°F, 20°C=68°F, 30°C=86°F. Interpolate between them.
- −40 is −40 on both scales — the one point where they meet, handy as a sanity check.
What about Kelvin?
Kelvin is the scientific scale: K = °C + 273.15. It starts at absolute zero (0 K = −273.15°C), so there are no negative temperatures — convenient for physics, irrelevant for weather. Our converter includes Kelvin alongside both everyday scales.
Oven temperatures, gas marks, and fan ovens
Recipes add two more scales to the temperature puzzle. Gas marks (UK tradition): Gas 4 = 350°F = 180°C; each gas mark ≈ 25°F / ~10–15°C. The handy sequence: Gas 1 (275°F/140°C), Gas 3 (325°F/170°C), Gas 4 (350°F/180°C), Gas 6 (400°F/200°C), Gas 7 (425°F/220°C).
Fan/convection ovens circulate hot air and cook faster — reduce the stated conventional temperature by 20°C (about 35°F). A recipe calling for 200°C conventional needs 180°C fan. Ignore this and the outside burns before the inside cooks; it is the most common unit-adjacent baking failure.
Also note: home ovens routinely run 10–25°F off the dial. An inexpensive oven thermometer ($10) tells you the truth about your specific oven — more valuable than any conversion table for actual results. Convert the recipe with our unit converter, verify with the thermometer, and adjust for fan.
Beyond the kitchen, temperature conversion matters most in weather and travel. A forecast of 35°C means serious heat (95°F) — hydration and shade weather — while 5°C (41°F) means a proper jacket. Americans visiting Europe and Europeans visiting the US constantly misjudge these: 70°F sounds cool to a Celsius native until they realize it is a pleasant 21°C. Memorize the anchor table above and you will never be caught underdressed.
One more scale worth knowing: wind chill and heat index ("feels like" temperatures) adjust the raw number for wind and humidity. A 0°C day with strong wind can feel like −8°C on exposed skin — which is why forecasts show both. The conversion math stays the same; only the input changes. Dress for the feels-like number, not the thermometer — your comfort depends on what your skin experiences, not what the sensor reports. With the formulas, the table, and the mental shortcuts above, you now have temperature conversion fully handled.
Temperature is one of four categories in the unit converter (length, weight, temperature, data). For the bigger picture on measurement systems, read metric vs. imperial.