Recipe says fan → conventional oven
Add 20°C to the fan temperature, then convert. Where the conventional °C is a row of the standard gas-mark table, the °F column shows that row's pairing; otherwise (*) it shows the nearest stop on a 25°F dial, with the exact figure alongside.
| Fan °C | Conventional °C | °F to set | °F exact | Gas mark |
|---|---|---|---|---|
| 120°C fan | 140°C | 275°F | 284°F | 1 |
| 130°C fan | 150°C | 300°F | 302°F | 2 |
| 140°C fan | 160°C | 325°F | 320°F | 3 |
| 150°C fan | 170°C | 350°F* | 338°F | 4 (nearest) |
| 160°C fan | 180°C | 350°F | 356°F | 4 |
| 170°C fan | 190°C | 375°F | 374°F | 5 |
| 180°C fan | 200°C | 400°F | 392°F | 6 |
| 190°C fan | 210°C | 400°F* | 410°F | 6 (nearest) |
| 200°C fan | 220°C | 425°F | 428°F | 7 |
| 210°C fan | 230°C | 450°F | 446°F | 8 |
| 220°C fan | 240°C | 475°F* | 464°F | 9 (nearest) |
| 230°C fan | 250°C | 475°F* | 482°F | 9 (nearest) |
* Not a row of the gas-mark table used here — nearest 25°F dial stop to the exact conversion. (Which?'s table lists gas mark 9 as 240°C / 475°F; this site's table uses 245°C.)
Conventional recipe → fan oven
A US recipe in °F, baked in a fan oven: convert to the recipe's °C, then subtract 20°C. If your oven is a US convection range set in °F, the manufacturer rule is different and smaller — 25°F lower (LG) — shown in the last column.
| Recipe °F | Recipe °C | Fan °C | Gas mark | US convection °F |
|---|---|---|---|---|
| 250°F | 120°C | 100°C | ½ | 225°F |
| 275°F | 140°C | 120°C | 1 | 250°F |
| 300°F | 150°C | 130°C | 2 | 275°F |
| 325°F | 160°C | 140°C | 3 | 300°F |
| 350°F | 180°C | 160°C | 4 | 325°F |
| 375°F | 190°C | 170°C | 5 | 350°F |
| 400°F | 200°C | 180°C | 6 | 375°F |
| 425°F | 220°C | 200°C | 7 | 400°F |
| 450°F | 230°C | 210°C | 8 | 425°F |
| 475°F | 245°C | 225°C | 9 | 450°F |
| 500°F | 260°C | 240°C | above 9 | 475°F |
Why fan ovens are set lower
A fan oven isn't hotter than its dial. It cooks faster at the same setting because the fan moves hot air across the food, and moving air transfers heat faster than still air — so the setting comes down instead. In the UK the convention is 20°C: the Which? oven temperature conversion table puts every fan temperature 20°C below its conventional row, and Hoover's fan-oven advice gives the same 20°C. A 20°C difference is 36°F — one Celsius degree is 1.8 Fahrenheit degrees (NIST).
US convection ovens use a smaller rule. LG tells owners to reduce a standard recipe by 25°F (14°C) for convection bake, and its ranges do that automatically — auto conversion is on by default. So on a US range, check the display before adjusting: 350°F entered may already bake at 325°F.
Before you adjust
- Your oven's manual overrides the chart. Manufacturers state their own fan or convection offset; follow it when it differs.
- Fan recipe, fan oven: no change. Only convert a fan temperature when your oven has no fan.
- Don't double-convert. Hoover: fan ovens can generally be set 20°C lower, and long cooking times can be shortened by up to 10 minutes per cooking hour — check the food is done. Don't take a further 20°C off a range that already auto-converts.
- Off the gas scale. Fan temperatures above 230°C convert to more than 250°C conventional, hotter than gas mark 9 (475°F); use a gas oven's highest setting.