Every other conversion here is a simple multiplication. Temperature is different because the two scales have different zero points as well as different degree sizes. Water freezes at 0°C and 32°F; it boils at 100°C and 212°F. So there are 100 Celsius degrees where there are 180 Fahrenheit degrees, giving the 9/5 ratio, and the scales are offset by 32.
| Celsius | Fahrenheit | What it is |
|---|---|---|
| -40°C | -40.0°F | same in both scales |
| -18°C | -0.4°F | typical freezer |
| 0°C | 32.0°F | water freezes |
| 10°C | 50.0°F | |
| 16°C | 60.8°F | |
| 20°C | 68.0°F | room temperature |
| 25°C | 77.0°F | |
| 30°C | 86.0°F | |
| 37°C | 98.6°F | human body |
| 40°C | 104.0°F | hot bath |
| 100°C | 212.0°F | water boils at sea level |
| 180°C | 356.0°F | moderate oven |
| 200°C | 392.0°F | hot oven |
| 220°C | 428.0°F | very hot oven |
The mental shortcut
Double it and add 30. For 20°C that gives 70°F against a true 68°F. The error grows as you move away from ordinary air temperatures — at 100°C it gives 230 against a true 212 — but for weather it is accurate to within a couple of degrees and takes no effort.
Going the other way: subtract 30 and halve. 70°F → 20°C, true value 21.1°C.
The one worth memorising is −40°C = −40°F. The scales cross there, and it is the only point where they agree.
Differences do not convert the same way
This trips people up. If a temperature rises by 10 Celsius degrees, that is a rise of 18 Fahrenheit degrees — not 50. For a difference you apply only the ratio and drop the offset:
So a fever running 1.5 C degrees above normal is 2.7 F degrees above normal. Any time you are converting a change, a range, or a tolerance rather than a reading, leave the 32 out.
Oven temperatures and gas marks
| Celsius | Fahrenheit | Gas mark | Description |
|---|---|---|---|
| 140°C | 275°F | 1 | very slow |
| 150°C | 300°F | 2 | slow |
| 170°C | 325°F | 3 | warm |
| 180°C | 350°F | 4 | moderate |
| 190°C | 375°F | 5 | fairly hot |
| 200°C | 400°F | 6 | hot |
| 220°C | 425°F | 7 | very hot |
| 230°C | 450°F | 8 | very hot |
| 240°C | 475°F | 9 | hottest |
A fan-assisted (convection) oven cooks faster. The usual guidance is to reduce the stated temperature by about 20 C degrees, so a recipe calling for 180°C conventional becomes roughly 160°C fan. This is a cooking adjustment, not a unit conversion — and oven thermostats are often out by more than the adjustment, so use an oven thermometer if it matters.
Kelvin
Kelvin uses the same degree size as Celsius but starts at absolute zero: K = °C + 273.15. There are no negative kelvins and no degree symbol — it is "300 kelvin", not "300 degrees Kelvin". Absolute zero is −273.15°C or −459.67°F.
Temperature conversion Celsius, Fahrenheit and Kelvin, with the formula shown for every conversion.
Open the converter