The Oven Temperature Conversion Formulas, Explained
Fahrenheit and Celsius are two different scales for the same physical temperature, offset by 32 degrees and scaled by 5/9. Converting between them is pure arithmetic:
| Conversion | Formula |
|---|---|
| Fahrenheit → Celsius | °C = (°F − 32) × 5/9 |
| Celsius → Fahrenheit | °F = (°C × 9/5) + 32 |
| Gas mark → Fahrenheit | °F = 275 + (Gas − 1) × 25 |
The gas mark is a UK scale tied to Fahrenheit: Gas 1 sits at 275°F and each mark adds 25°F, so Gas 4 is 350°F, Gas 6 is 400°F, and Gas 9 is 475°F. Because the steps are uniform in Fahrenheit, the matching Celsius values don't land on tidy numbers — Gas 1 is exactly 135°C, and Gas 9 is 246°C. Our converter rounds to the nearest whole degree, which is more precision than any oven dial actually provides.
Step-by-Step Example: Converting 180°C
Cakes, cookies, and pastries are usually baked at 180°C — here's how the conversion plays out.
- Convert Celsius to Fahrenheit: 180 × 9/5 + 32 = 356°F.
- Find the nearest gas mark: (356 − 275) ÷ 25 + 1 = 4.24, which rounds to Gas 4.
- Read the results: 180°C = 356°F = Gas 4.
Most recipes and cookbook tables round 356°F down to 350°F — both are correct in practice, since the converter reports the exact value while recipes use the nearest conventional setting. Enter 180 into the calculator above with °C selected to confirm.
Reference Table: Common Oven Temperatures
| °F | °C (exact) | Gas Mark | Common Description |
|---|---|---|---|
| 250°F | 121°C | ½ | Very slow — meringues, slow roasts |
| 275°F | 135°C | 1 | Very slow — slow-cooked meats |
| 300°F | 149°C | 2 | Slow — braises, cheesecakes |
| 325°F | 163°C | 3 | Slow-moderate — casseroles, brownies |
| 350°F | 177°C | 4 | Moderate — cakes, cookies, most baking |
| 375°F | 191°C | 5 | Moderate — pastries, breads, roasting |
| 400°F | 204°C | 6 | Moderately hot — roast chicken, vegetables |
| 425°F | 218°C | 7 | Hot — roasting, pizza |
| 450°F | 232°C | 8 | Hot — searing, thin-crust pizza |
| 475°F | 246°C | 9 | Very hot — broiling, quick roasts |
Some cookbooks also use quarter- and half-marks (Gas ¼, ½) for very slow cooking below 275°F. Our converter reports anything below Gas 1 as "cool oven" — for those recipes, use the Fahrenheit or Celsius value directly.
Fan Oven (Convection) Temperature Adjustments
| Conventional Oven | Fan Oven (approx.) | Gas Mark |
|---|---|---|
| 325°F / 163°C | 300°F / 149°C | Gas 2–3 |
| 350°F / 177°C | 325°F / 163°C | Gas 3–4 |
| 375°F / 191°C | 350°F / 177°C | Gas 4–5 |
| 400°F / 204°C | 375°F / 191°C | Gas 5–6 |
| 425°F / 218°C | 400°F / 204°C | Gas 6–7 |
These are starting points, not laws — the exact reduction depends on your oven's airflow, how full it is, and what you're cooking. When in doubt, drop the temperature and check for doneness a few minutes early; you can always return food to a hot oven, but you can't un-bake it.
Troubleshooting & Practical Tips
Calibrating an Oven That Runs Hot or Cold
The temperature on the dial is rarely the temperature inside. Consumer ovens commonly drift 15–25°F from their setting, and that drift grows with age. If your cakes consistently over- or under-bake, an oven thermometer on a middle shelf is a cheap way to learn your oven's true temperature — then use the converter to translate recipes to your oven's reality. Many modern ovens also have a built-in calibration offset you can adjust in the settings menu, which fixes the error at the source rather than making you mentally add or subtract degrees at every recipe.
Fan (Convection) Ovens
Fan ovens circulate air and cook faster and more evenly than conventional ovens. Most recipes assume a conventional oven; for a fan oven, reduce the temperature by about 25°F (or 15°C) and check the food several minutes early. Because the heat is more uniform, trays can often be crowded more closely without uneven baking.
High-Altitude and Large Batches
At high altitude, water boils at a lower temperature and baked goods rise differently — many bakers raise the oven temperature slightly and shorten bake times. Large or crowded batches also extend baking time regardless of temperature. These are cooking adjustments, not conversion errors; the math above is exact for any temperature on any scale.
Common Mistakes to Avoid
- Adding or subtracting 32 in the wrong direction — Fahrenheit is the larger number for everyday oven temperatures.
- Applying the 5/9 ratio the wrong way: 1°C is 1.8°F, so a 20°C change equals a 36°F change.
- Assuming gas marks convert evenly to Celsius — they step evenly in Fahrenheit only.
- Ignoring fan-oven adjustments and then blaming the conversion when food burns.