Gas mark 4 is 350°F, or 180°C. That's the one number worth memorising. Most everyday baking recipes sit at gas mark 3 to 5.
Gas mark is a dial-position scale used on gas ovens in the UK, Ireland, and several Commonwealth countries. It isn't a temperature unit itself, it's a manufacturer's numbering for oven dial settings that happens to map onto real temperatures. American recipes use Fahrenheit directly, and most of the rest of the world bakes in Celsius. This chart lines all three up.
| Gas mark | Fahrenheit | Celsius | Heat |
|---|---|---|---|
| 1/4 | 225°F | 110°C | Very cool |
| 1/2 | 250°F | 120°C | Very cool |
| 1 | 275°F | 140°C | Cool |
| 2 | 300°F | 150°C | Cool |
| 3 | 325°F | 160°C | Warm |
| 4 | 350°F | 180°C | Moderate |
| 5 | 375°F | 190°C | Moderately hot |
| 6 | 400°F | 200°C | Hot |
| 7 | 425°F | 220°C | Hot |
| 8 | 450°F | 230°C | Very hot |
| 9 | 475°F | 240°C | Very hot |