A fan circulates hot air, so many recipes suggest a lower setting than for a conventional oven. A common guide is to subtract 20 °C from the stated conventional Celsius temperature: 180 becomes about 160 fan, 200 becomes about 180 fan, and 220 becomes about 200 fan. This is a cooking convention, not an exact physical conversion. Oven design, fan strength, food load, and recipe testing all affect the suitable setting.
Apply minus 20 °C only as a starting point
For a recipe written at 200 °C conventional, 180 °C fan is a sensible initial interpretation when no fan instruction is supplied. It does not claim that every fan oven transfers heat identically. Some manufacturers recommend a different reduction, some recipes keep the same heat but shorten time, and delicate bakes can react strongly. OvenTemp labels the value approximate and never calls it an exact equivalent.
The recipe and appliance instructions take priority
When the recipe says “180 °C fan,” set 180 °C fan; do not subtract another 20 degrees. When it lists both conventional and fan values, use its tested pair. Check the appliance manual for mode symbols and conversion advice because “fan,” “convection,” and fan-assisted modes may heat differently. The general rule is most useful only when a conventional recipe gives no fan alternative at all.
Adjust with time and doneness, not blind arithmetic
Begin checking a little earlier when moving an unfamiliar recipe to a fan oven, especially for thin biscuits, pastries, and small portions. Use the recipe’s visual, texture, or internal-temperature signs when provided. Avoid repeatedly opening the door, which changes the oven environment. Record what worked for your appliance in your own notes. OvenTemp does not monitor cooking and cannot replace safe food-temperature guidance or a calibrated oven thermometer.