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Oven Temperatures Explained: °C, °F, Gas Mark, Thermostat
Four scales describe the same oven heat — Celsius, Fahrenheit, the British gas mark and the French thermostat. They were never designed to match, so every equivalence is an approximation.
The anchor point: thermostat 6
If you memorize one equivalence, make it this: thermostat 6 is 180 °C, exactly 356 °F, and the counterpart of gas mark 4 — which recipes conventionally write as 350 °F. It is the default « moderate oven » for cakes, cookies and most roasting, and the pivot of every temperature table.
The main tiers
The French thermostat climbs in 30 °C steps (thermostat = degrees ÷ 30), while the gas mark advances in irregular steps of roughly 10 to 20 °C.
- Thermostat 3: 90 °C / 194 °F — very slow oven
- Thermostat 4: 120 °C / 248 °F — slow
- Thermostat 5: 150 °C / 302 °F — gas mark 2 — gentle
- Thermostat 6: 180 °C / 356 °F — gas mark 4 — moderate, the standard
- Thermostat 7: 210 °C / 410 °F — between gas marks 6 and 7 — hot
- Thermostat 8: 240 °C / 464 °F — gas mark 9 — very hot
- Thermostat 10: 300 °C / 572 °F — maximum, for pizza and flatbreads
Why the numbers never quite line up
Gas marks and thermostats are tiers, not formulas — each mark covers a range of real temperatures. That is why the same 180 °C shows as exactly 356 °F on the thermostat table but a round 350 °F beside gas mark 4, and why thermostat 5 and gas mark 2 share 150 °C yet print 302 °F and 300 °F. Converting between tiers means finding the nearest published step, not doing arithmetic — a converter maps each value to the closest real tier.
A fan oven runs hotter than the dial
The fan pushes hot air against the food instead of letting it stratify, so a convection oven heats more efficiently at the same setting. The standard correction is to lower the set temperature by about 20 °C: a recipe written for 180 °C conventional becomes 160 °C fan. Watch recipes already labelled « fan » or « convection » — the correction applies once, not twice.
Reading an old or foreign recipe
British recipes of any era speak in gas marks; mid-century American books say « slow », « moderate » or « hot » (roughly 150, 180 and 220 °C); French recipes think in thermostats. Convert to the scale your oven speaks, take the nearest tier rather than splitting the difference, and let an oven thermometer settle arguments — domestic ovens are often off by 10 °C or more.