Fan Oven vs Conventional Oven
What a fan actually changes, how to adjust a recipe written for a conventional oven, and when the temperature is not the thing to change.
The short answer
A fan oven runs hotter in effect than the number on the dial suggests, because moving air transfers heat to food far more efficiently than still air. The usual UK adjustment is to set a fan oven about 20°C lower than a recipe written for a conventional oven.
To convert a temperature either way: Fan Oven Converter
Equivalent temperatures
| Conventional | Fan | Fahrenheit | Gas mark |
|---|---|---|---|
| 140°C | 120°C fan | 285°F | Gas 1 |
| 160°C | 140°C fan | 320°F | Gas 3 |
| 180°C | 160°C fan | 355°F | Gas 4 |
| 190°C | 170°C fan | 375°F | Gas 5 |
| 200°C | 180°C fan | 390°F | Gas 6 |
| 220°C | 200°C fan | 430°F | Gas 7 |
| 240°C | 220°C fan | 465°F | Gas 9 |
Produced by the same converter used on the oven temperature calculator.
For gas marks in either direction, or Fahrenheit from an American recipe, use the Oven Temperature and Gas Mark Converter.
What the fan actually changes
Speed of heat transfer. Food browns and cooks faster at the same dial setting, which is why the setting comes down.
Evenness. A fan oven has far less difference between shelves, so two trays cook much more alike than in a conventional oven.
Drying. Moving air dries surfaces. That is excellent for roast potatoes and chicken skin, and unhelpful for anything that wants to stay moist and pale.
When not to drop the temperature
Modern recipes and UK packaging usually give a fan figure already, often labelled “fan” or “180°C fan”. Dropping that by another 20°C undercooks the food. If the recipe names fan explicitly, use it as printed.
Some things prefer the fan off even in a fan oven: delicate cakes and meringues, which can crack or colour unevenly, and anything covered in a lid or foil where air movement has no effect anyway.
Does the time change too?
If you drop the temperature by 20°C, the time stays roughly the same. That is the whole point of the adjustment. If you keep the conventional temperature in a fan oven instead, expect it to be done noticeably sooner and start checking early.
Every cooking-time calculator on this site asks whether your oven is fan or conventional and takes it into account, so there is no separate conversion step. Try it on Chicken Cooking Time or Beef Roasting Time.
Air fryers are a third case
An air fryer is a small, very aggressive fan oven. It is not simply “fan minus 20”: the small chamber and high air speed mean both temperature and time usually come down.
To convert an oven recipe for an air fryer: Air Fryer Converter
Common mistakes
Converting a figure that was already fan. Check the label before adjusting.
Trusting the dial. Domestic ovens are often 10 to 20°C out. An oven thermometer is the cheapest cooking upgrade there is.
Not preheating. Fan or not, the time only counts once the oven is at temperature.
Last reviewed 11 September 2026. How we work out the numbers.
Calculators used in this guide
Related guides
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- How to Roast BeefChoosing a joint, searing, rare through to well done, why beef is timed differently from chicken, and how long to rest it.
- Cake Tin Sizes and Recipe ScalingHow to bake a recipe in the tin you actually own: matching area rather than width, adjusting batter quantity, and what happens to the baking time.