Oven Temperatures: °F, °C and Gas Marks Explained

Half the world's recipes say 180°C, the American ones say 350°F, and the British gas-oven ones say gas mark 4 — all describing the same gentle bake for a cake or a tray of roast vegetables. Moving between the three systems is mostly one exact formula plus one quirky stepped dial, with a convection wrinkle that every modern kitchen now has to think about.

Two exact scales and one stepped dial

Fahrenheit and Celsius convert precisely, in either direction: °C = (°F − 32) × 5⁄9, and back again °F = °C × 9⁄5 + 32. So 350°F is 176.7°C, 180°C is 356°F, and water's two anchor points — 32°F = 0°C and 212°F = 100°C — make sanity checks easy. This is the same math as any temperature conversion; ovens add no physics, only context.

Gas marks are different: they are not a continuous scale but named steps on a British gas-oven dial. Mark 1 is 275°F, and each whole mark adds 25°F, so mark 4 is 350°F, mark 6 is 400°F, and the top of the ladder, mark 10, is 500°F. Below mark 1 hang two fractional settings: ½ is 250°F and ¼ is 225°F for the slowest meringues and drying work.

Snapping to the nearest mark

Because gas marks only exist in 25°F steps, most converted temperatures land between rungs. 180°C becomes 356°F, which is 6°F above mark 4's 350°F — so recipes call it gas mark 4, and the 6°F gap is far smaller than the swing of any real oven. A converter's job is to snap to the nearest mark and admit when the match is approximate: 350°F is exactly mark 4, while 190°C (374°F) sits close enough to mark 5 (375°F) that the difference is academic. Below about 212°F or above 512°F there is no mark to snap to at all, so an honest converter leaves the field empty rather than inventing one.

Running the ladder in reverse is exact by construction: mark 6 is 250 + 25 × 6 = 400°F, which is about 204°C, so an electric oven can follow the Fahrenheit or Celsius equivalent of any gas-mark recipe directly.

Fan ovens: the −25°F / −20°C habit

Convection (fan) ovens blow hot air across the food, constantly replacing the insulating layer of cool air that surrounds it. Heat transfer increases, and food behaves as if the air were roughly 15–20°C hotter than the dial reads. The universal response is not to trust the timer but to lower the set temperature: American convention subtracts 25°F from the conventional setting, British guidance subtracts 20°C. The two are not identical — 25°F is about 14°C — but both encode the same practice, and both land close enough that the cake does not care.

So a recipe's 350°F conventional becomes 325°F fan; its 180°C conventional becomes 160°C fan. Note that the conversion runs in the unit family of the recipe: subtracting 20°C from a Fahrenheit-native recipe would mean converting twice and drifting from the published US guidance. When converting systems and switching to fan, convert first, then adjust — one operation at a time keeps the rounding errors visible and small.

Practical notes for converted recipes

Three habits make converted recipes behave. First, trust an oven thermometer over the dial: ovens routinely run 10–25°F off their set point, which dwarfs the rounding in any °F/°C conversion. Second, when a recipe gives a range ("180–190°C"), pick the lower end the first time you bake it converted, then adjust once with evidence. Third, remember that convection also browns faster, so check color early even when the thermometer says the temperature is right — the fan adjustment handles energy, not Maureen the Maillard reaction's enthusiasm.

Try it yourself

The Oven Temperature Converter handles all three systems in one panel: enter a temperature in °F, °C or gas mark and get the full row — Fahrenheit, Celsius, the nearest gas mark (with exact-or-approximate noted), and the fan-assisted setting under both the US and UK conventions. For general temperature conversion outside the kitchen — weather, science, thermostats — the Temperature Converter covers the full range of scales.