To convert Celsius to Fahrenheit, multiply the temperature by 9/5 and add 32. Written as a formula, that is degrees F = (degrees C × 9/5) + 32, where 9/5 is the same as 1.8. For example, 20 °C × 1.8 = 36, and 36 + 32 = 68 °F. That single formula covers every conversion from freezer to oven.
The formula, step by step
Take any Celsius temperature and do two operations in order:
- Multiply the Celsius value by 9/5 (or 1.8).
- Add 32 to the result.
Say you have 25 °C. Multiply by 1.8 to get 45, then add 32 for 77 °F. The multiply-then-add order matters; adding 32 first would give the wrong answer. To reverse the process and go from Fahrenheit to Celsius, subtract 32 first and then multiply by 5/9: degrees C = (degrees F − 32) × 5/9.
Common temperatures chart
| Celsius | Fahrenheit | Reference point |
|---|---|---|
| -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 (sea level) |
Oven-temperature chart
Oven dials are where most cooks need this conversion. The exact Fahrenheit value is on the left; the rounded setting American recipes typically use is on the right, along with the UK gas mark.
| Celsius | Fahrenheit (exact) | Rounded oven setting | Gas mark |
|---|---|---|---|
| 140 °C | 284 °F | 275 °F | 1 |
| 150 °C | 302 °F | 300 °F | 2 |
| 170 °C | 338 °F | 325 °F | 3 |
| 180 °C | 356 °F | 350 °F | 4 |
| 190 °C | 374 °F | 375 °F | 5 |
| 200 °C | 392 °F | 400 °F | 6 |
| 220 °C | 428 °F | 425 °F | 7 |
| 230 °C | 446 °F | 450 °F | 8 |
The rounding is deliberate: oven dials move in 25-degree steps in the US, so 356 °F becomes the nearest mark at 350 °F. The small difference will not affect most baking.
A quick mental shortcut
When you just need a ballpark, double the Celsius number and add 30. For 20 °C that gives 70 °F, close to the true 68 °F. The shortcut works because doubling approximates the 1.8 multiplier and 30 stands in for 32. The error grows at higher temperatures, so for oven settings, candy making, or anything where a few degrees matter, use the full formula instead.
Why the scales differ
The two scales were built around different reference points. Anders Celsius set 0 and 100 at the freezing and boiling points of water, giving a 100-degree span. Daniel Fahrenheit used a different zero and a finer degree, so water freezes at 32 and boils at 212, a 180-degree span. Dividing 180 by 100 gives the 9/5 ratio in the formula, and the 32 accounts for the offset zero. That is the whole reason the conversion needs both a multiply and an add. Understanding this also makes the reverse direction intuitive: to undo the formula you reverse the order of operations, subtracting the 32 offset before dividing out the 9/5 scaling. The single point where the two scales cross, -40 degrees, is where the offset and the scaling happen to cancel out exactly.
Worked examples
Running the formula on a few everyday temperatures:
- 30 °C on a hot day: 30 × 1.8 = 54, plus 32 = 86 °F.
- 4 °C, a typical fridge setting: 4 × 1.8 = 7.2, plus 32 = 39.2 °F.
- 160 °C for a gentle roast: 160 × 1.8 = 288, plus 32 = 320 °F.
- -18 °C, a standard freezer: -18 × 1.8 = -32.4, plus 32 = -0.4 °F, essentially 0 °F.
Each takes two steps and a moment of arithmetic, and the freezer example shows the formula handles negative numbers the same way. If you cook or travel often between the two systems, it is worth memorizing a handful of these anchors so you can sanity-check any conversion at a glance and catch an obvious slip before it ruins a dish.
Fan (convection) ovens
One practical note for baking: a fan or convection oven circulates hot air and cooks faster, so recipes often tell you to lower the temperature. A common guideline is to reduce a conventional Celsius setting by about 20 degrees for a fan oven, then convert to Fahrenheit if your dial uses it. For example, a conventional 180 °C becomes roughly 160 °C fan, which is about 320 °F. Always convert first from the temperature the recipe specifies, then apply any fan-oven adjustment, rather than doing both at once and losing track of which number you started from.
Keep it handy
For cooking, the values worth memorizing are 180 °C = 350 °F for a standard bake and 100 °C = 212 °F for boiling. Everything else you can derive in seconds with the formula. If your recipe also mixes volume units, our guides to how many cups are in a liter and how many milliliters are in a cup cover the other common metric-to-US conversions you are likely to hit in the same recipe.
