Gas Mark

Gas Mark is a British oven temperature scale introduced in the 1940s by gas-appliance manufacturers to standardise oven dial labels. It runs from Mark 1/4 (very slow, ~225°F / 110°C) through Mark 9 (very hot, 475°F / 246°C), increasing by 25°F (~14°C) per mark above Mark 1.

The standard reference table:

• Mark 1/4 — 225°F / 110°C — very slow
• Mark 1/2 — 250°F / 120°C — very slow
• Mark 1 — 275°F / 135°C — slow
• Mark 2 — 300°F / 150°C — slow
• Mark 3 — 325°F / 165°C — moderately slow
• Mark 4 — 350°F / 180°C — moderate (the default)
• Mark 5 — 375°F / 190°C — moderate
• Mark 6 — 400°F / 200°C — moderately hot
• Mark 7 — 425°F / 220°C — hot
• Mark 8 — 450°F / 230°C — very hot
• Mark 9 — 475°F / 246°C — very hot

Gas Mark is rare in modern UK appliances (electric and induction ovens label in °C) but still common in cookbooks from before the metric transition, and in some older gas ranges. Convert any of the three scales with our oven temperature converter.

Worked example

A British roast-chicken recipe specifies “Gas Mark 7 for 20 minutes, then drop to Gas Mark 5 for 1 hour.” Mark 7 = 425°F = 220°C; Mark 5 = 375°F = 190°C. On a US electric oven, set initially to 425°F, after 20 minutes drop to 375°F. The 30°C drop is what gives the chicken a high-heat browning phase followed by gentler cooking — overshoot the second temperature and the meat dries before the centre reaches 75°C internal. If the same recipe is being cooked in a fan oven (convection), adjust both numbers down by 20°C: bake at 200°C for 20 min, then 170°C — equivalent to dropping each by one Gas Mark. Bakers cooking sourdough in a domestic oven that maxes out at “Gas Mark 9 / 475°F” can’t reach the ~250°C (Mark 9 high end) that high-hydration recipes specify, which is why professional bread ovens running at 260-280°C produce a crust home ovens never match.

When and why it matters

Gas Mark matters most when reproducing recipes from older British cookbooks (Delia Smith, pre-1990 Mary Berry, original Mrs Beeton) and from regional UK community publications that never adopted Celsius. The mistake to avoid is interpreting “Mark 4” from an American republication of a British recipe — sometimes the editor has misconverted, sometimes the temperatures are correct but the recipe assumed a non-fan oven the modern reader is using as a fan oven. The safest practice: ignore the Mark number, read the Celsius value next to it, then apply your own fan/non-fan adjustment. For ovens with broken thermostats (more common than people realise — a 30-year-old gas range can drift 20°C off), an oven thermometer placed on the rack and recalibrated every few months is the only way to trust any temperature, Gas Mark or otherwise. Reference: BBC Food — Oven temperatures and Gas Marks.

Why deliberately non-numeric?The Gas Mark scale was introduced precisely to discourage cooks from second-guessing the oven’s thermostat calibration. In the 1940s, mass-produced gas ovens varied by ±20°F between units of the same model — labelling a dial “400°F” implied a precision the appliance didn’t deliver. Marking positions as “Mark 6” instead let the manufacturer publish a temperature range (~390-410°F) without misrepresenting the dial as a calibrated instrument. The same logic kept the scale numeric but coarse — half-mark precision is a finer adjustment than the oven’s thermostat can reliably hold anyway.

Fan-assisted oven adjustment:the published Gas Mark table assumes a conventional (non-fan) oven. Fan-assisted ovens circulate air more efficiently and effectively cook at 20-25°C (≈35-45°F) hotter than the dial reads. The standard adjustment is to drop the Gas Mark by one (or the temperature by 20°C) when adapting a non-fan recipe for a fan oven, or to raise it when going the other direction. UK recipe writers increasingly publish both numbers — “180°C / 160°C fan / Gas Mark 4” — for this reason. Related: oven temperature converter, Maillard reaction.