A fan (convection) oven circulates hot air with a fan, so heat reaches your food faster and more evenly than in a conventional oven, where hot air just rises. The practical consequence: a fan oven cooks as if it were about 20°C / 25°F hotter than its dial says. Recipes are written for conventional ovens unless they say otherwise, so fan-oven bakers need to translate.
The conversion chart
| Conventional | Conventional °C | Fan oven °C | Gas mark |
|---|---|---|---|
| 300°F | 150°C | 130°C | 2 |
| 325°F | 165°C | 145°C | 3 |
| 350°F | 175°C | 155°C | 4 |
| 375°F | 190°C | 170°C | 5 |
| 400°F | 200°C | 180°C | 6 |
| 425°F | 220°C | 200°C | 7 |
| 450°F | 230°C | 210°C | 8 |
| 475°F | 240°C | 220°C | 9 |
Reduce temperature or reduce time?
You have two valid options, and they suit different bakes. Reducing the temperature (the chart above) keeps the baking time roughly as written and is the safer default for delicate items — cakes, custards, anything that needs gentle, even setting. Keeping the temperature and cutting the time by roughly 10–20% suits things that benefit from aggressive heat: roasted vegetables, pastry that needs color. Pick one adjustment, not both — doing both is the classic route to an underbaked center.
When the fan helps — and when to turn it off
The fan is your friend for multiple trays at once (it evens out the hot spots that make one tray of cookies brown before another), for crisping, and for anything where surface color is the goal. It's less kind to delicate batters: the moving air can ripple cheesecake tops, lean sponge cakes, and soufflés, and it dries meringues' surfaces before their insides set. If your oven lets you switch the fan off, do so for those — and use the conventional setting your recipe assumed.
Trust a thermometer over the dial
Whatever oven you have, the dial is a suggestion. Home ovens routinely run 15–25°F away from their setting, and that offset — not your technique — explains a lot of chronically overdone cookies. An inexpensive oven thermometer tells you the truth once, and then every recipe gets easier.
Baking a recipe that also needs resizing? The recipe scaler handles the ingredients while the chart above handles the heat.