Gas marks are a temperature scale used in older British, Irish, and some Australian recipes. They measure oven heat by gas flow rate rather than degrees, which is why they don't map neatly onto Celsius or Fahrenheit values.
Complete Gas Mark Conversion Table
| Gas Mark | °C | Fan °C | °F | Heat Description |
|---|---|---|---|---|
| ¼ | 120 | 100 | 250 | Very cool |
| ½ | 130 | 110 | 265 | Very cool |
| 1 | 140 | 120 | 275 | Very low |
| 2 | 150 | 130 | 300 | Low |
| 3 | 165 | 145 | 325 | Warm |
| 4 | 180 | 160 | 350 | Moderate |
| 5 | 190 | 170 | 375 | Moderately hot |
| 6 | 200 | 180 | 400 | Hot |
| 7 | 220 | 200 | 425 | Very hot |
| 8 | 230 | 210 | 450 | Extremely hot |
| 9 | 245 | 225 | 475 | Maximum |
How Gas Marks Work
Gas marks represent the size of the gas valve opening in a gas oven. Gas Mark 1 is the lowest cooking heat, Gas Mark 9 is the highest. The scale was standardised in the early 20th century in the UK.
When You'll Encounter Gas Marks
Gas marks appear in older British cookbooks (pre-1980s), traditional Irish recipes, and some Australian vintage recipes. Modern UK recipes almost always use Celsius alongside gas marks: "180°C/160°C fan/Gas Mark 4."
The "Moderate" Benchmark
The most important landmark: Gas Mark 4 = 180°C = 350°F. This is the most common baking temperature, and it's the one to memorise. Most cakes, cookies, and breads fall in the Gas Mark 4–6 range (180–200°C / 350–400°F).
Fan Oven Adjustment
Always reduce by 15–20°C for a fan oven. Gas Mark 4 (180°C) becomes 160–165°C in a fan oven.