Fan Oven vs Conventional Oven Temperatures

Two kinds of oven, one recipe

A conventional oven heats from elements at the top and bottom, or from a gas burner, and the air inside moves only by natural convection. A fan oven, also called a convection oven, adds a fan that circulates the hot air around the food. Many modern electric ovens are fan-assisted, and the US uses the word “convection” for the same feature.

The difference matters because recipes are written with one type in mind. A temperature that is correct for a conventional oven can brown a dish too quickly in a fan oven, and the reverse can leave food paler and slower than expected.

Why a fan changes the result

Moving air carries heat to the surface of the food more efficiently than still air. The surface browns and crisps sooner, and moisture on the outside evaporates faster. It also evens out hot and cold spots, so trays on different shelves cook more alike.

The effect is similar to the way a breeze makes a cold day feel colder than the thermometer says. The air temperature has not changed, but heat leaves or enters the surface faster.

The thermostat of a fan oven reports the temperature of the air, but the food experiences that air more intensely. This is why the same number on the dial gives a stronger effect with the fan running, and why manufacturers and baking guides suggest a lower setting.

The usual adjustment

The common rule in British guidance is to set a fan oven about 20 °C lower than the temperature given for a conventional oven. In Fahrenheit, a reduction of 25 °F is the usual rule of thumb. The two are close, since 20 °C is 36 °F and 25 °F is about 14 °C, so treat them as approximate guides rather than exact equivalents.

Some ovens and some manufacturers recommend a different figure, such as 10 to 20 °C, or advise shortening the cooking time instead. If your oven manual states its own advice, follow it over any general rule. The reduction is a starting point, not a guarantee, because fan strength and oven size differ from model to model, and a first bake in a new oven is a good chance to note how it behaves.

Worked examples

Here is the 20 °C rule applied to common temperatures, going from a conventional setting to a fan setting:

• 160 °C conventional becomes 140 °C fan.
• 180 °C conventional becomes 160 °C fan.
• 200 °C conventional becomes 180 °C fan.
• 220 °C conventional becomes 200 °C fan.

In Fahrenheit, the 25 °F rule turns 350 °F into 325 °F and 400 °F into 375 °F. Going the other way, a recipe that says “160 °C fan” should be set to 180 °C if your oven has no fan, which corresponds to gas mark 4.

Reading the recipe’s wording

Check how the recipe states its temperature before changing anything. Many British recipes print both figures, for example “180 °C / 160 °C fan / gas mark 4”. In that case, simply use the number that matches your oven and make no further adjustment. Printing both figures is the clearest way for a recipe to avoid confusion.

If only one number is given, look for clues. A recipe that says nothing about a fan is often written for a conventional oven, but not always, and some modern sources assume a fan oven by default. When in doubt, begin with the lower fan setting and check early. Gas mark charts describe conventional gas ovens, so a gas mark does not include a fan reduction.

Checking time as well as temperature

Lowering the temperature is the main correction, but cooking time can shift too. Because fan ovens transfer heat faster, some dishes finish a little sooner even at the reduced setting. Start checking a few minutes before the recipe’s stated time and judge by the signs it describes, such as color, firmness or a skewer that comes out clean.

Roasted vegetables and pastry tend to benefit from the extra airflow, as it helps them crisp. Delicate batters and very light sponges can be more sensitive, and some cooks turn the fan off or use the conventional mode for them when the oven offers that choice. Large items such as a whole roast are less affected, because the heat still has to travel to the center, so they are usually judged by internal doneness as the recipe or label directs.

Doing the conversion by hand

Fan adjustments are a separate step from unit conversion. A temperature converter such as the one on this site changes degrees Celsius, degrees Fahrenheit and gas marks into one another, but it does not subtract the fan reduction for you. The sensible order is to convert the recipe’s temperature into the unit your oven uses and then apply the fan reduction yourself.

For example, a recipe that calls for 350 °F in a conventional oven converts to about 177 °C, which is normally rounded to 180 °C. For a fan oven you would then set 160 °C. Because ovens vary in how accurately they hold temperature, an inexpensive oven thermometer can show whether your dial is reliable.