Last updated: 2026-06-28

Oven Temperature and Gas Mark

Gas marks are a temperature scale used on gas ovens sold in the United Kingdom and Ireland. Because different oven types — gas, electric conventional, and fan (convection) — operate at different effective temperatures for the same setting, cooks regularly need to convert between them. This calculator takes a conventional oven temperature and returns the equivalent gas mark and fan oven setting.

The gas mark scale

The gas mark scale dates to the early twentieth century, when domestic gas ovens became widespread in Britain. The scale runs from gas mark ¼ (107°C / 225°F, described as "very cool") to gas mark 9 (246°C / 475°F, described as "very hot"). Gas mark 4 — 180°C (356°F) — is the most commonly called-for setting in recipes, roughly equivalent to a moderate oven.

The reference table below lists the complete scale:

How the conversion works

The gas mark scale follows an approximately linear progression. The conversion formula anchors at 121°C (gas mark 0) and steps up by 14°C per mark:

$\text{Gas mark} = \text{round}\!\left(\frac{T_{\text{°C}} - 121}{14}\right)$

For a conventional oven set to 180°C:

$\text{Gas mark} = \text{round}\!\left(\frac{180 - 121}{14}\right) = \text{round}(4.21) = 4$

The fan oven equivalent subtracts 20°C (roughly 36°F):

$T_{\text{fan}} = T_{\text{conventional}} - 20\text{°C}$

Fan ovens vs. conventional ovens

A fan oven (convection oven) uses an internal fan to circulate heated air throughout the cavity. This eliminates hot spots and distributes heat more evenly than a static, conventionally heated oven. The result is a more consistent bake and — because moving air transfers heat more efficiently than still air — an effectively higher cooking temperature at the same dial setting.

The standard guidance is to reduce the temperature by about 20°C (36°F) when switching from a conventional to a fan oven, or to shorten the cooking time by roughly 10 to 15 percent. In practice, the exact reduction depends on the oven model, so the manufacturer's handbook or a tested recipe is the most reliable guide.