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Fan ovens cook about 20C hotter than the dial suggests, so recipes written for conventional ovens are reduced by 20C. American recipes are in Fahrenheit.
What The Oven Temperature Converter Works Out
- Fan oven: the conventional temperature minus 20C. Moving air transfers heat faster, so a fan (convection) oven runs about 20C cooler on the dial for the same effect. This is the adjustment that ruins the most dinners: older books and most American recipes assume conventional heat.
- Fahrenheit: Celsius x 9/5 + 32, rounded to the recipe-friendly 25 degree steps. An American recipe that says "350 degrees" without units means Fahrenheit, which is 180C, not a kiln.
- Gas mark: the traditional UK scale climbing in 25F intervals. Gas 4 (180C, 350F) is the classic moderate oven most baking recipes assume; gas 6 (200C) is the roasting setting.
- Exact temperature (advanced): type any figure in conventional Celsius, fan Celsius or Fahrenheit instead of picking from the list. The converter works out the other scales exactly and names the nearest standard setting, so a US recipe at 325F resolves to 163C conventional, 143C fan, gas 3.
- Set your dial to (advanced): the single figure to use on your own oven, whether fan, conventional or gas, after correcting for how far it runs hot or cool. Real ovens drift from their dials by 10C to 20C and have hot spots; a cheap freestanding oven thermometer settles the question and is the best upgrade for consistent baking.
- Air fryer (advanced): the conventional temperature minus 20C, with the time cut by about a fifth; air fryers are small, fast fan ovens.
- Trust the cues: when a recipe misbehaves at the stated setting, trust the visual cues and the thermometer over the dial, and use the middle shelf unless the recipe says otherwise.