Oven Temperature Converter

Common oven temperatures

The formula

Fahrenheit and Celsius are two linear scales measuring the same thing, so converting between them is a single expression with no lookup involved. The fan setting is then a fixed offset applied to the conventional temperature, and the last step rounds everything to the nearest 5 degrees.

That rounding is part of the calculation rather than a display flourish. An oven that steps in fives and holds its setpoint by cycling an element cannot act on a fractional degree, so carrying one through would be false precision dressed up as accuracy.

°C = (°F − 32) × 5/9
°F = °C × 9/5 + 32
fan = conventional − 25 °F, or − 20 °C
displayed = round(value ÷ 5) × 5

Worked example: a recipe says 400 °F conventional. The exact conversion is (400 − 32) × 5/9 = 204.44 °C, which rounds to 205 °C. For a fan oven, the Fahrenheit figure drops to 400 − 25 = 375 °F, and the Celsius figure to 204.44 − 20 = 184.44 °C, which rounds to 185 °C. A UK gas-mark chart would call the same setting gas 6 and print it as 200 °C.

That last gap is worth understanding rather than resolving. The gas-mark chart is a trade convention built for tidy Celsius dials, so it pairs 400 °F with 200 °C and 350 °F with 180 °C even though the exact conversions are 204.4 °C and 176.7 °C. Neither number is wrong; one favours arithmetic and the other favours a chart you can read at a glance, and the difference between them is smaller than the variation between two ovens set to the same mark.

The fan offset is a convention too, and a different one on each side of the Atlantic. This tool reduces by 25 °F on the Fahrenheit side and by 20 °C on the Celsius side, following the American and British rules of thumb respectively rather than converting either into the other. Those are not identical cuts: 20 C° is a slightly deeper reduction than 25 F°. Neither is a measurement, and if your oven still browns fast after the reduction, take another 5 degrees off — your own oven is the authority.

How to use the oven temperature converter

Enter the temperature, pick the unit your recipe uses, and read it back in the other scale. Tick the fan or convection box and you also get the lower number to actually dial in. Every figure is rounded to the nearest 5 degrees, which is deliberate: oven dials and digital pads step in fives, gas marks step in much larger jumps than that, and a domestic oven holds its setpoint by switching the element on and off, so the true internal temperature is always moving around the number on the front. Converting 356 °F to 180 °C to the exact degree would imply a level of control that no home oven offers, so the display stops where the equipment does.

The fan adjustment exists because a convection oven moves air, and moving air carries heat to the surface of food faster than still air does. The oven is not hotter; the heat simply arrives more quickly, so the same number on the dial browns and cooks as though it were higher. The fix is a fixed reduction, and the size of it is a local convention rather than a physical constant. American recipes say to drop 25 °F. British ovens and cookbooks say to drop 20 °C, and Which? states that fan oven cooking temperatures are typically around 20 °C less than conventional ones. Those two are not the same cut — 25 Fahrenheit degrees is only 13.9 Celsius degrees — so this converter follows each scale on its own terms rather than converting one into the other. Read the Fahrenheit output if you cook in Fahrenheit and the Celsius output if you cook in Celsius, and you get the advice your own kitchen tradition actually gives.

Gas marks are a third scale again, and they are conventions rather than conversions. The standard UK chart pairs gas mark 4 with 350 °F and 180 °C, gas 6 with 400 °F and 200 °C, gas 9 with 475 °F and 240 °C. Run the arithmetic and those Celsius figures do not check out: 350 °F is really 176.7 °C, and 400 °F is 204.4 °C. The chart rounds to tidy round numbers that suit a Celsius dial, which is why a recipe converted from Fahrenheit and a recipe converted from a gas-mark chart can disagree by a few degrees and both be correct. Neither difference is larger than the swing your oven produces on its own.

Finally, do not fan everything. The moving air that browns a roast chicken, crisps potatoes and lets you bake three trays of cookies at once is rough on anything delicate. Custards, cheesecakes, soufflés, meringues, choux and tall sponge cakes prefer gentle, still heat, and a draft can crack the top, dry the edges or lift one side of a cake higher than the other. For those, switch to the conventional bake setting and use the unreduced temperature. And if precise temperature genuinely matters to your baking, an inexpensive oven thermometer tells you more than any conversion can, because a great many ovens simply do not hold the number on the dial.

Frequently asked questions