Oven Temperature Conversions Made Simple: Celsius, Fahrenheit, Gas Mark and Fan
By the Super Simple Digital Tools Team · Updated June 2026
Few things stall a recipe faster than an oven temperature in the wrong units. A brownie recipe says 325F, your oven only shows Celsius, and a different recipe insists on gas mark 3. They are very likely the same heat, but unless you know the relationships, you are stuck guessing. The good news is that oven scales line up on a small number of well-known reference points, and once you know how the four systems map to each other, every recipe becomes readable on your own dial.
Start with the two metric and imperial scales. Celsius and Fahrenheit are linked by a fixed formula: multiply Celsius by 1.8 and add 32 to get Fahrenheit, or subtract 32 and divide by 1.8 to go the other way. In practice, cooks lean on memorable anchor points rather than doing the sum each time. The most useful is 350F equals 180C, the everyday moderate oven, with 400F around 200C for hotter roasting and crisping, and 425 to 450F around 220 to 230C for pizza, bread, and high-heat browning.
Gas marks are the scale most likely to confuse anyone outside the UK. The system is simple once decoded: gas mark 1 sits at 275F (about 140C), and each step up the scale adds 25F. That makes gas mark 4 the moderate 350F (180C) standard, gas mark 6 a hotter 400F (200C), and gas mark 9 a fierce 475F (240C) for searing and quick browning. Below gas mark 1 there are fractional settings, 1/4 and 1/2, sitting around 225 and 250F for low, slow cooking.
Fan, or convection, ovens add one more wrinkle. Because a fan circulates hot air, heat reaches the food faster and more uniformly than in a still conventional oven. The widely used rule of thumb is to set a fan oven about 20C (roughly 35 to 40F) lower than a recipe written for a conventional oven, so a 180C conventional bake becomes 160C fan. If you ignore this, the outside of a cake or roast can over-brown before the centre is done. Manufacturers vary, so treat 20C as a reliable default rather than an absolute law.
One last quirk explains why conversion charts never quite match a calculator. Oven dials only offer round numbers, so charts deliberately round to settings you can actually select. The exact conversion of 350F is closer to 177C, but every chart shows 180C; 425F is technically about 218C but appears as 220C. These small roundings are harmless in baking, where a few degrees rarely matter, and they make the numbers usable. When precision counts, such as delicate meringues or tempering, trust an oven thermometer over the dial, since most ovens run several degrees off their setting anyway.
- Memorize one anchor pair, 350F equals 180C equals gas mark 4, and you can estimate most other settings by stepping 25F or about 14C at a time.
- Drop 20C (or about 35 to 40F) for a fan oven, and check your food a few minutes early since it will also cook faster, not just at a lower number.
- Keep an inexpensive oven thermometer inside the cavity; many home ovens are 10 to 25 degrees off their dial, which matters more than any rounding in a chart.
- For low-and-slow cooking or dehydrating, use gas mark 1/4 to 1/2 (about 110 to 120C / 225 to 250F) rather than the lowest normal baking setting.