How much lower is a fan oven than a conventional one?

About 20°C lower for the same result. A recipe at 180°C conventional is cooked at 160°C fan. Some ovens need 25°C less, some only 15°C, so adjust to your own oven and verify with an oven thermometer.

What is Gas Mark 4 in Celsius and Fahrenheit?

Gas Mark 4 is 180°C, which is 356°F (usually written as 350°F in American recipes). It is the most common baking temperature for cakes, biscuits and roasts.

Why do recipes give two temperatures like 180°C/160°C fan?

Because the same recipe works in a conventional or a fan oven, and the fan setting is 20°C lower. The first number is for conventional ovens, the second for fan-assisted ones. Use the one that matches your oven.

My oven runs hot — should I convert differently?

No — convert the recipe normally, then adjust the dial down by the amount your oven runs hot, using an oven thermometer to find the real temperature. The conversion is about the recipe’s intent; the thermometer is about your oven’s reality.

Cooking & DIY/Home Calculators

Oven Temperatures Including Fan Settings

Oven temperature is the conversion that most often ruins a bake, because the scales look interchangeable but are not. A recipe at 180°C, 350°F, Gas Mark 4 and 160°C fan are all roughly the same oven — but reading one as another means a 30°C error and a ruined result. This guide explains the four scales, how they relate, and how to move any recipe onto the oven you actually own.

Pair it with the Oven Temperature Converter to convert a specific figure. The core idea is that every scale reduces to a conventional Celsius value, and the fan setting is simply conventional minus about 20°C.

In detail

Celsius and Fahrenheit: the basic conversion

Celsius is the metric temperature scale used in most of the world; Fahrenheit is used in the United States. They convert exactly: °C = (°F − 32) × 5/9, and °F = °C × 9/5 + 32. The common baking equivalents are 180°C = 356°F (often rounded to 350°F), 200°C = 392°F (400°F), and 160°C = 320°F. Because ovens step in roughly 10°C increments and thermostats are imprecise, recipes round to the nearest 5 or 10 degrees, so a converted temperature within 5°C of the target is effectively identical.

Gas mark: the British scale

Gas mark is a British temperature scale for gas ovens, running from ¼ to 9. Each mark maps to a fixed Celsius value: Mark 1 = 140°C, 2 = 150, 3 = 165, 4 = 180, 5 = 190, 6 = 200, 7 = 220, 8 = 230, 9 = 240. Gas ovens cannot be set between marks, so a converted temperature is rounded to the nearest mark. Marks ¼ (110°C) and ½ (120°C) exist for very slow ovens, used for meringues and drying. If a recipe gives a Celsius value between marks, pick the nearest one — a 10°C difference is within an oven’s normal swing.

Fan ovens: conventional minus 20

A fan-assisted (convection) oven blows hot air across the food, transferring heat more efficiently than the still air in a conventional oven. To get the same cooking result, recipes set a fan oven about 20°C lower than a conventional one: 180°C conventional becomes 160°C fan, 200°C conventional becomes 180°C fan. Some ovens need 25°C less, some only 15°C, so 20°C is a convention rather than a rule. Many modern recipes give both temperatures (e.g. 180°C/160°C fan) for exactly this reason.

Reading a recipe written for another oven

When a recipe gives a temperature in a scale your oven does not have, convert it to conventional Celsius first, then to your oven’s scale. A US recipe at 350°F becomes 177°C conventional (round to 180°C), then 160°C fan if you have a convection oven, or Gas Mark 4 if you have a gas oven. The Oven Temperature Converter does all of this from a single input. Always preheat fully — the thermostat light going off means the oven has reached its set point, not that the walls are fully soaked with heat.

Oven thermometers and real temperatures

Oven thermostats are imprecise: many ovens run 10–25°C off their setting, and the temperature swings as the element cycles on and off. A cheap oven thermometer placed in the centre of the oven tells you the real temperature and lets you adjust the dial to match. For baking where 10°C matters — bread, meringues, macarons — an oven thermometer is the single most useful tool you can buy, more useful than any conversion. Convert the recipe, then verify with the thermometer.

Frequently asked questions

How much lower is a fan oven than a conventional one?: About 20°C lower for the same result. A recipe at 180°C conventional is cooked at 160°C fan. Some ovens need 25°C less, some only 15°C, so adjust to your own oven and verify with an oven thermometer.
What is Gas Mark 4 in Celsius and Fahrenheit?: Gas Mark 4 is 180°C, which is 356°F (usually written as 350°F in American recipes). It is the most common baking temperature for cakes, biscuits and roasts.
Why do recipes give two temperatures like 180°C/160°C fan?: Because the same recipe works in a conventional or a fan oven, and the fan setting is 20°C lower. The first number is for conventional ovens, the second for fan-assisted ones. Use the one that matches your oven.
My oven runs hot — should I convert differently?: No — convert the recipe normally, then adjust the dial down by the amount your oven runs hot, using an oven thermometer to find the real temperature. The conversion is about the recipe’s intent; the thermometer is about your oven’s reality.

Related calculators

Concept guide based on standard temperature conversions, the British gas mark table (Mark 1–9), and the 20°C fan-oven convention. Last updated: September 2026.

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