Oven temperature converter
Celsius, Fahrenheit, gas mark and fan. The gas scale is defined in Fahrenheit and the Celsius column is a rounding that published charts disagree about — so both are shown. Nothing you type here leaves your browser — it is worked out on your own device, so there is nothing to send and nothing to log.
The gas mark scale is defined in Fahrenheit
Exactly, and simply: gas mark n is 250 + 25n degrees Fahrenheit. Mark 1 is 275°F, mark 4 is 350°F, mark 9 is 475°F, and every mark is twenty-five degrees from the next one all the way up. Below mark 1 the scale continues as ½ (250°F) and ¼ (225°F).
The Celsius column is not a conversion, and two published tables disagree about it
Gas mark 3 is 325°F. Convert that properly and you get 162.8°C, which is not a number anybody would print in a recipe. So the Celsius column in every oven chart is a rounding — and the rounding is a convention, not arithmetic, which is why the charts do not agree:
| Which? says | gas mark 3 = 160°C |
|---|---|
| Wikipedia says | gas mark 3 = 170°C |
| The actual conversion | 325°F = 162.8°C, between the two |
Neither table is wrong, and both are in print. Every other converter on the internet picks one silently. This one shows both, and shows the exact conversion beside them so you can see why the question has two answers. Ten degrees Celsius is not nothing in a cake, but it is a great deal less than the difference between where your oven says it is and where it actually is.
Fan ovens: twenty degrees, by convention
A fan moves hot air over the food instead of waiting for it to arrive, so a fan oven cooks faster at the same dial setting. The usual advice, and what Which? prints, is to set a fan oven 20°C lower than a conventional one. Some manufacturers say 25°F, some say 15°C, and the only authority that matters is the manual for your oven. It is a convention here and labelled as one.
Your oven is lying to you by more than any of this
Domestic ovens routinely run twenty or thirty degrees Celsius away from the dial, and vary by as much again between the top shelf and the bottom. An oven thermometer costs less than a bag of flour and will tell you more than any conversion table. If your cakes are always slightly wrong, that is where to look first.
What it will not do
- It will not adjust a cooking time. Temperature and time are not interchangeable — a lower oven for longer is a different result, not the same one slower.
- It will not know your oven. See above.
- It will not go above gas mark 10 or below gas mark ¼, because the scale does not.