Oven Temperatures: Gas Marks, Fan Ovens and the 25-Degree Problem

A recipe gives you 350°F. Your oven is marked in Celsius, it is a fan oven, and your grandmother's version of the same recipe says gas mark 4. All three are the same temperature, and none of them is the number you should set.

The whole table

Gas mark	Conventional °C	Fan °C	°F	What it is for
¼	110	90	225	Meringues, very slow drying
1	140	120	275	Slow braising, casseroles
2	150	130	300	Slow roasting
3	170	150	325	Rich fruit cakes
4	180	160	350	The default for almost everything
5	190	170	375	Sponges, biscuits
6	200	180	400	Roasting vegetables, pastry
7	220	200	425	Bread, hot roasting
8	230	210	450	Pizza, scones
9	240	220	475	As hot as most domestic ovens go

Convert any temperature not in the table with the Celsius to Fahrenheit converter or Fahrenheit to Celsius.

Why 350°F is sometimes 175 and sometimes 180

Run the arithmetic and 350°F is 176.67 °C. Neither 175 nor 180.

British recipes settled on 180 °C because oven dials are marked in tens and gas mark 4 had to land somewhere. American recipes converted into metric often say 175 °C, because it is the nearer round number. The gap is three degrees on a domestic oven that probably cannot hold temperature to within ten. Use whichever your dial makes easy.

This is worth knowing mainly so you stop worrying about it. A cake does not know the difference between 175 and 180. It very much knows the difference between 180 and 200.

The fan oven rule

A fan (convection) oven moves hot air across the food, which transfers heat considerably faster than still air. Set to the same number, it cooks hotter and quicker.

Subtract 20 °C from any conventional temperature. So a recipe calling for 180 °C conventional wants 160 °C in a fan oven.

Some manufacturers say 25 °C and some say 20. The difference does not matter for anything except delicate baking. What matters is doing it at all: a fan oven set to the recipe's conventional temperature runs roughly one gas mark hot, which is enough to brown a cake's crust before the middle has set.

Alternatively, keep the temperature and cut the time by about 25% — useful for roasting, where a harder exterior is welcome, and poor for cakes, where it is not.

Many modern ovens are marked with both a fan symbol and a conventional one, and the displayed number means different things in each mode. If a dish that always worked suddenly browns too fast, check which mode the dial is in before blaming the recipe.

Your oven is probably not the temperature it says

Domestic oven thermostats are commonly out by 10–20 °C, and ovens have hot spots — usually the back, usually the top. A cheap oven thermometer left on the middle shelf will tell you more about your baking than any conversion table.

If everything browns on one side, the fix is turning the tray halfway through, not adjusting the temperature.

The quick version

• Fan oven: recipe temperature minus 20 °C
• Gas mark 4 = 180 °C = 350°F, and each mark up is roughly 10–20 °C
• 175 vs 180 °C: it does not matter
• Preheat properly — most ovens signal "ready" several minutes before the walls are

And if you are working from an American recipe, the oven temperature is the easy part. The cups are the problem: see why American recipes fail in a UK kitchen.