Oven Temperature: Converting Between Fahrenheit, Celsius, Gas Marks, and Fan Settings

You pull a recipe off the internet, it says 350°F, and your oven dial only goes by degrees Celsius. Or it says "gas mark 4" and you have never owned a gas oven in your life. Or the recipe was clearly written for a conventional oven and you have a fan oven, and somewhere in the back of your mind a voice says you are supposed to turn the dial down but you cannot remember by how much. Cooking should not require mental arithmetic over a bowl of dough, so let me walk through how oven temperatures actually translate across the four systems you will meet, and where the easy mistakes hide.

The two scales: Fahrenheit and Celsius

Most of the confusion starts here. The United States bakes in Fahrenheit. Nearly everywhere else, and all of science, uses Celsius. They describe the exact same heat, just with different numbers on the dial. The conversion is one formula:

°C = (°F − 32) × 5/9

Going the other way, °F = °C × 9/5 + 32. The two anchor points worth memorising are that water freezes at 0°C / 32°F and boils at 100°C / 212°F. Everything else falls on a straight line between and beyond those.

In practice you rarely need the formula by hand, because the common baking temperatures cluster around a few familiar pairs. 325°F is about 165°C, 375°F is about 190°C, 425°F is about 220°C. The one that shows up most often is 350°F, which works out to 176.7°C. Almost nobody sets their oven to 176.7, so recipes round it to 175°C or 180°C, and both are close enough that your cake will not know the difference.

What a gas mark actually is

British gas ovens do not show degrees on the dial. They show numbers, roughly 1 through 9, called gas marks. It is not an arbitrary scale — each number corresponds to a real temperature:

Gas mark 1 ≈ 140°C
Gas mark 4 ≈ 180°C ≈ 350°F (the everyday baking setting)
Gas mark 9 ≈ 240°C

The catch that trips people up: the scale is not perfectly linear. Below gas mark 5 the steps are 10°C apart, and above it they jump to 20°C apart. So the gap between gas 4 and gas 5 is 10°C, but the gap between gas 8 and gas 9 is 20°C. That means gas mark 9 (240°C) is genuinely much hotter than a naive "9 is just over twice 4" reading would suggest. If you ever inherit a vintage British cookbook written entirely in gas marks, do not eyeball it — convert each one.

The reason gas mark 4 is the unofficial default for cakes, biscuits and roast vegetables is precisely that it lands on 180°C, which is also the rounded value of 350°F. Three systems, one moderate oven.

Why fan ovens run hotter, and what to do about it

A conventional oven heats by radiation and natural air movement from the element. A fan (or convection) oven adds a fan that circulates the hot air, which means the food surface meets a higher effective heat than the dial number implies. Hot air moving across the food transfers energy faster than still hot air at the same temperature.

The rule of thumb everyone in a professional kitchen knows: a fan oven runs about 20°C hotter, so lower the dial by roughly 20°C (about 25°F) below whatever a conventional recipe states. A recipe at 200°C conventional becomes 180°C on a fan oven. One written for 350°F becomes about 325°F fan. Cooking time often shortens a little too, since the food is heating faster, so start checking a few minutes before the recipe says it is done.

This single adjustment is behind the most common complaint I see from people switching ovens: "my fan oven burned it." They followed the conventional number directly, the surface cooked 20°C too hot, and the top of the tray scorched while the middle was still going. Drop the dial and the problem disappears.

A worked example: 350°F across all four systems

Let me run the most common temperature through every system, the way you would if you were standing at the oven.

Start with 350°F. Apply the formula: (350 − 32) × 5/9 = 318 × 5/9 = 176.7°C, which rounds to 180°C in practice. Because 180°C is gas mark 4, that is your gas setting. And if you have a fan oven, drop it by 20°C: 160°C fan (or about 325°F fan).

So a single American instruction of "bake at 350°F" becomes, for everyone else: 180°C conventional / gas mark 4 / 160°C fan. Write all four on the recipe card once and you never have to think about it again. That is exactly what good recipe blogs do — they list every system so no reader has to do the maths mid-bake. If you also need to resize the batch while you are at it, the recipe scaler handles ingredient quantities so the whole recipe stays proportional.

Following recipes from other countries

Once you can move freely between the four systems, foreign recipes stop being intimidating. A French recipe that says "four moyen" (moderate oven) means roughly 180°C. An American "hot oven" sits up near 220–230°C / 425–450°F. A British recipe at gas mark 6 is 200°C / 392°F. The vocabulary differs, the heat does not.

My own habit, after burning more than one tray of biscuits early on, is to convert the temperature the moment I start reading a recipe and pencil all the equivalents in the margin before I touch a single ingredient. It takes ten seconds and it removes the one decision I am most likely to get wrong when I am moving quickly with flour on my hands. I also note whether my fan setting applies, because the conventional-versus-fan slip is the one that actually ruins food rather than just making it slightly off.

For the quick conversion itself, the oven temperature converter takes any one of Fahrenheit, Celsius or gas mark and gives you the other two instantly, plus the fan-oven setting and a plain-language heat band so you can tell at a glance whether you are in "moderate" or "hot" territory. And if your day involves more than just oven heat — scaling a marinade, dividing a tray-bake — the general-purpose unit converter covers weights, volumes and lengths too.

The short version

Keep three facts and you can handle almost any recipe. First, °C = (°F − 32) × 5/9, and 350°F lands on 180°C, gas mark 4. Second, the gas-mark scale steps 10°C below gas 5 and 20°C above it, so do not read it as linear. Third, a fan oven runs about 20°C hotter, so lower the dial by 20°C whenever a recipe was written for a conventional oven. Get those three right and the burned tops, undercooked middles, and "wait, how hot is gas mark 6 again" moments mostly disappear.

Made by Toolora · Updated 2026-06-13