Oven Temperature Converter

Enter a temperature, pick whether it is Celsius, Fahrenheit or a gas mark, and the converter fills in the other scales along with the fan-oven setting. It answers the everyday question of what a recipe means when its number and your oven dial disagree. The default, 180 °C, is the temperature most baking and roasting recipes assume, and it has a name in every scale: 356 °F, gas mark 4, and a moderate oven in the language of older cookbooks.

How the scales relate

Celsius and Fahrenheit convert with a single line of arithmetic:

F = C × 9 ÷ 5 + 32

Gas marks are different. They are not degrees but a fixed lookup table that has been standard in British kitchens for decades, running from mark 1 at 140 °C to mark 9 at 245 °C. The fan-oven figure is simpler: take the conventional Celsius temperature and subtract 20.

Take the default, 180 °C. Multiply by 9 to get 1,620, divide by 5 to get 324, then add 32, which lands on 356 °F. That temperature is exactly gas mark 4, and a fan oven browns the same food at 160 °C, twenty degrees lower. So 180 °C, 356 °F, gas mark 4 and 160 °C fan all describe one oven, the setting a recipe means by a moderate oven.

Where the gas mark came from

The gas mark exists because early gas ovens were hard to control. When James Sharp patented a domestic gas cooker in Northampton in 1826 and began manufacturing in the town about a decade later, the oven had no thermostat: the cook opened and closed a valve by hand and judged the heat by feel, or by an old baker's trick such as watching how fast flour scattered on the oven floor darkened, or how long a strip of paper took to brown. Gas cookers lost out to the coal-fired kitchen range for decades, partly because that guesswork was so unforgiving, and only became a commercial success in England in the 1880s, once gas mains reached enough homes.

Automatic control changed that. The idea of a self-regulating heat source is old, and around 1620 the Dutch inventor Cornelis Drebbel built an egg incubator and furnace governed by a mercury-and-air regulator, in which warming air expanded, pushed a column of mercury and closed the damper. That principle reached the domestic oven only in the 1920s. Radiation Ltd, a British cooker maker, fitted its ovens with a thermostatic regulator it called the Regulo and launched it on the "New World" cooker, announced in press advertisements dated 13 May 1923. Set the pointer to a number, the advertising promised, and the oven would reach that heat and hold it without further attention. The numbers on that dial are the gas mark scale. Recipes carried the trade name for decades, and a 1943 cookery book still instructs the reader to bake at "Gas, Regulo Mark 7"; after the patent lapsed, cookery writers and public bodies dropped the brand, and "gas mark" standing on its own is first recorded in print in 1958. Regulo 4 and gas mark 4 name the same setting.

The numbers were chosen around Fahrenheit, the scale British kitchens used at the time. Gas mark 1 was set at 275 °F and each whole mark added 25 °F, so mark 2 is 300 °F, mark 3 is 325 °F and so on up the range, while below mark 1 the fractions a half at 250 °F and a quarter at 225 °F filled in the low, slow settings used for meringues and long braises. When British recipes went metric in the 1970s those Fahrenheit figures were rounded to convenient Celsius numbers, which is why printed charts disagree by a few degrees and why the modern table below is not perfectly even.

The two temperature scales behind it

Both degree scales predate the gas oven by a century and the numbered dial by two. Daniel Gabriel Fahrenheit, an instrument maker born in Danzig to a German family who spent his working life in the Dutch Republic, published his scale in 1724 using 32 for melting ice and 96 for blood heat, and he recorded water boiling at about 212 on it soon after. The tidy modern definition, freezing at exactly 32 and boiling at exactly 212 with 180 degrees between them, came later: a Royal Society committee including Henry Cavendish reported on the fixed points of thermometers in 1777. Anders Celsius, a Swedish astronomer, presented his hundred-degree scale to the Royal Society of Sciences in Uppsala in 1742; his original version ran the other way, with 0 for boiling and 100 for freezing, and it was inverted to its modern form the year after his death, a reversal usually credited to Carl Linnaeus. The awkward factor of 9 ÷ 5 in the formula is simply the ratio of those two spans, 180 Fahrenheit degrees against 100 Celsius degrees, and the plus 32 shifts the zero points into line.

Gas mark chart

The full table, with fan-oven equivalents rounded to the usual dial marks:

The steps are uneven because the marks were laid out in round Fahrenheit numbers, then rounded again into Celsius when British recipes went metric in the 1970s. One gas mark is exactly 25 °F, about 14 °C, but the rounded Celsius column moves by anywhere from 10 to 20 degrees per step, and published charts disagree: gas mark 3 is printed as 160 °C in some books and 165 °C in others. That is why the converter treats the gas column as a lookup rather than a formula.

The scale also stops at both ends. Below about 125 °C and above about 260 °C — roughly one mark past the 140 and 245 that bracket the table — the converter leaves the gas mark blank instead of pinning the reading to the nearest row, because no gas dial covers that heat. Celsius, Fahrenheit and the fan figure still convert as usual. The temperature field itself accepts 0 to 1000, which spans every oven setting in any of the three scales.

Working the numbers by hand

To go the other way, from Fahrenheit to Celsius, run the same steps backwards: subtract 32 first, then multiply by 5 and divide by 9. For 356 °F that is 356 − 32 = 324, then 324 × 5 ÷ 9 = 180 °C. Do the same with 425 °F, a common American roasting figure, and you get 393 × 5 ÷ 9 = 218.3 °C, which most cooks round to 220. The converter reports that one as gas mark 7, which is exactly what 425 °F was on the original Fahrenheit spacing. For gas marks the reliable move is to read the nearest row of the chart rather than calculate, because the metric rounding has broken the clean 25-degree Fahrenheit spacing the scale was born with.

Fan ovens and old recipe language

A fan, or convection, oven moves hot air across the food, so it cooks faster and more evenly than a conventional oven at the same dial reading. The standard fix is to drop the temperature by about 20 °C, or one to two gas marks, and check food a few minutes early. Manufacturers differ, so treat 20 °C as a starting point rather than a rule; fan ovens reached home kitchens long after the gas mark scale was settled.

Older cookbooks rarely print numbers at all, because they were written for ovens that had none. A slow oven is roughly 150 °C (gas mark 2), a moderate oven is 180 °C (gas mark 4), and a hot oven sits around 220 °C (gas mark 7). Those phrases still turn up in reprinted and handed-down recipes, and the chart above puts a number on each of them.

Which scale your recipe uses

Where a recipe was written usually tells you which number it means. American recipes almost always give Fahrenheit. British and Irish ones lean on gas marks, often printed alongside Celsius. Continental Europe, Australia, New Zealand and Canada work in Celsius, and continental recipes often name the oven setting as well as the number, so look for a fan or convection note before subtracting anything. When a recipe does not say, 180 °C or 350 °F is the safe reading for general baking.

Oven dials and thermostats drift over time, so treat every converted figure as a starting point and confirm that food is cooked through with a calibrated thermometer, especially for meat and poultry. See the site disclaimer.

Frequently asked questions

What is gas mark 4 in Celsius and Fahrenheit?

Gas mark 4 is 180 °C or 356 °F, the moderate-oven setting most general baking and roasting recipes assume. In a fan oven, drop it to 160 °C. Each step up or down the gas scale is roughly a 10 to 20 degree Celsius change.

How much lower should I set a fan oven?

Reduce a conventional temperature by about 20 °C, so 200 °C becomes 180 °C fan and 180 °C becomes 160 °C fan. That is one to two gas marks down. Ovens vary, so check food a few minutes early the first time you convert a recipe.

What temperature is a moderate oven?

A moderate oven is 180 °C, 356 °F or gas mark 4. A slow oven is about 150 °C (gas mark 2) and a hot oven is around 220 °C (gas mark 7). These descriptive terms come from older cookbooks written before dials were marked in degrees.

Is gas mark used outside the UK?

Gas marks are mainly a British and Irish convention. Recipes from the United States use Fahrenheit, while continental Europe, Australia, New Zealand and Canada use Celsius. The gas mark scale runs from 1 at 140 °C up to 9 at 245 °C.

How do I convert Celsius to Fahrenheit for an oven?

Multiply the Celsius figure by 9, divide by 5 and add 32. For 200 °C that is 200 × 9 ÷ 5 + 32 = 392 °F. Oven recipes are usually rounded to the nearest 5 or 10 degrees, so 392 °F often appears as 390 °F or 400 °F.