Fan Oven Temperature Conversion Chart: The 20°C Rule Made Simple
Most UK recipes are still written for conventional ovens, yet most kitchens now run a fan model. Set the dial too high and the outside of your food cooks before the middle is ready. This guide gives you the full conversion chart and the one simple rule that keeps your baking and roasting on track.
A recipe that says 200°C means 180°C on a fan setting. That single adjustment covers almost everything you will cook.
Oven temperature conversion chart
This table converts between conventional Celsius, fan Celsius, gas mark and Fahrenheit, so you can follow any UK recipe whatever scale it uses. The fan column is the one to set if your oven circulates air.
| Conventional (°C) | Fan (°C) | Gas mark | Fahrenheit (°F) | Description |
|---|---|---|---|---|
| 140 | 120 | 1 | 275 | Cool |
| 150 | 130 | 2 | 300 | Cool |
| 160 | 140 | 3 | 325 | Moderate |
| 180 | 160 | 4 | 350 | Moderate |
| 190 | 170 | 5 | 375 | Moderately hot |
| 200 | 180 | 6 | 400 | Moderately hot |
| 220 | 200 | 7 | 425 | Hot |
| 230 | 210 | 8 | 450 | Hot |
| 240 | 220 | 9 | 475 | Very hot |
Worth a bookmark for everyday cooking. The three conversions people look up most often are below.
The 20°C rule explained
The rule is straightforward: take the conventional temperature printed in your recipe and lower it by 20°C when you cook in a fan oven. So 180°C becomes 160°C, and 200°C becomes 180°C. There is no need to recalculate for every dish, because the gap stays the same right across the range.
The one exception is a recipe that already gives a fan figure. Modern UK recipes increasingly do, and some list two temperatures, a higher one for conventional ovens and a lower one for fan. If a single temperature is given with no explanation, it is usually safest to assume it was written for a fan oven, since that is what most homes now use. When in doubt, the recipe wording tells you which scale you are working from.
Why fan ovens run cooler
A fan oven has a fan at the back, often paired with its own ring heating element, that pushes hot air around the cavity. That moving air transfers heat to food faster than the still air of a conventional oven and removes the cooler pockets that form away from the elements. The result is more even cooking that reaches the food more quickly, which is exactly why a lower dial setting produces the same finish.
This is also why fan models suit batch baking and multi shelf cooking so well. If you want the full picture of how the airflow works and where it helps most, our guide on how a fan oven works goes deeper, and true fan versus fan assisted baking explains the difference between the two fan settings you may see on your control panel.
Temperature or timing, not both
There are two ways to adjust a conventional recipe for a fan oven. The simplest is to drop the temperature by 20°C and leave the cooking time as written. The alternative is to keep the temperature the same and shorten the cooking time by roughly 10 percent instead.
The important point is to choose one method, not both. Lowering the temperature and cutting the time together overcorrects, and you can end up with food that is pale and underdone. For most home cooking, reducing the temperature is the easier and more reliable option, especially for baking where timing matters less than steady heat.
Is your oven actually accurate
The chart assumes your oven hits the temperature you set, and not every oven does. Consumer testing regularly finds models that overshoot or undershoot their target, sometimes by a wide margin, and a cake that burns at the correct setting is often a sign the oven is running hot rather than a fault in your method.
A separate stainless steel oven thermometer is the quickest way to check. Place it in the centre of the oven, leave it for at least ten minutes at a set temperature, then compare the reading with the dial. If the gap is small you can simply adjust the setting up or down to compensate. If it is large or the temperature swings during cooking, the calibration is worth investigating. Understanding the different heat modes also helps, which our complete oven functions guide covers symbol by symbol.
Quick summary
- For a fan oven, lower the conventional recipe temperature by 20°C. So 200°C becomes 180°C.
- The 20°C gap holds across the whole range, so you never need to recalculate per dish.
- If a recipe already gives a fan temperature, use it as written and skip the adjustment.
- Adjust either the temperature or the timing, never both, or the food will undercook.
- Check your oven with a separate thermometer if results are consistently too dark or too pale.
Frequently asked questions
180°C conventional is gas mark 4, which is 160°C in a fan oven. Gas mark 4 is the most common baking temperature for cakes and biscuits.
Only when the recipe was written for a conventional oven. If the recipe already states a fan temperature, set that figure as printed. Where two temperatures are given, the lower one is for fan ovens.
No. Choose one adjustment. Either drop the temperature by 20°C and keep the time, or keep the temperature and cut the time by about 10 percent. Doing both will leave food underdone.
Yes. The circulating air heats food more quickly and more evenly than still air, which is why a lower temperature setting gives the same result as a hotter conventional oven.
Many ovens run hotter or cooler than the dial suggests. If bakes are consistently too dark, check the real temperature with a separate oven thermometer and adjust the setting to suit.
The conversion figures and the 20°C fan adjustment in this guide are confirmed by the UK consumer body Which?, whose own oven temperature conversion table makes a handy second reference to keep alongside this one.
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