Oven Temperature Conversion Chart
Celsius, Fahrenheit, gas mark and fan oven equivalents in one table. Most charts give you two of the four.
The chart
| Gas mark | Fahrenheit (exact) | Celsius (as printed) | Celsius (exact) | Fan oven | Description |
|---|---|---|---|---|---|
| Gas mark 1/4 | 225 | 110 | 107.2 | 90 | Very cool |
| Gas mark 1/2 | 250 | 120 | 121.1 | 100 | Very cool |
| Gas mark 1 | 275 | 140 | 135.0 | 120 | Cool |
| Gas mark 2 | 300 | 150 | 148.9 | 130 | Cool |
| Gas mark 3 | 325 | 160 | 162.8 | 140 | Warm |
| Gas mark 4 | 350 | 180 | 176.7 | 160 | Moderate |
| Gas mark 5 | 375 | 190 | 190.6 | 170 | Moderately hot |
| Gas mark 6 | 400 | 200 | 204.4 | 180 | Hot |
| Gas mark 7 | 425 | 220 | 218.3 | 200 | Hot |
| Gas mark 8 | 450 | 230 | 232.2 | 210 | Very hot |
| Gas mark 9 | 475 | 240 | 246.1 | 220 | Very hot |
Two Celsius columns, because they differ. The gas mark scale is defined in Fahrenheit, so those values are exact. The Celsius column recipes actually print is a rounded convention, and converting it back gives a figure a few degrees off. Gas mark 1 is exactly 275 °F, which is 135.0 °C, but every British recipe writes it as 140 °C. Neither is wrong; the rounding is baked into the convention. Fan oven values apply the 20 °C reduction explained below. For any other value use the Celsius to Fahrenheit converter.
Fan ovens and the 20 degree rule
A fan oven, also called a convection oven, circulates hot air rather than relying on it to move on its own. Moving air transfers heat to food faster, so the same dial setting cooks harder. The widely used correction is to set a fan oven about 20 °C, or roughly 25 °F, lower than a conventional recipe specifies.
Apply one adjustment, not both. The other common correction is to keep the temperature and cut the cooking time by around 10 to 25 percent. Doing both at once overcorrects and is a frequent cause of undercooked centers. Pick the temperature reduction or the time reduction.
It's worth saying where this figure comes from: the 20 °C rule is a cooking convention reported consistently by flour producers, appliance guidance and recipe publishers, not a figure set by a standards body. Manufacturers differ, and some ovens apply their own offset internally. Your oven manual beats this chart.
Gas marks are perfectly linear, in Fahrenheit
Look at a gas mark chart in Celsius and the steps seem irregular: 140, 150, 160, 180, 190, 200, 220. Look at the same scale in Fahrenheit and it is exactly even.
gas mark 1/2 = 250 °F, gas mark 1/4 = 225 °F, continuing the same 25 °F step
Every whole gas mark sits exactly 25 °F above the one below it. Gas mark 4 is 250 + 100 = 350 °F. Gas mark 9 is 250 + 225 = 475 °F. The scale was calibrated in Fahrenheit by British cooker manufacturers in the 1920s and it is a clean arithmetic progression.
The apparent irregularity is an artefact of rounding those Fahrenheit values into Celsius for print. 325 °F is 162.8 °C, written as 160. 350 °F is 176.7 °C, written as 180. That jump from 160 to 180 looks like a bigger step than the others, and it isn't.
Which oven a recipe assumes
British and European recipes normally give Celsius, and often give both conventional and fan figures. Where only one Celsius number appears in a modern British recipe, it is increasingly the fan figure, since fan ovens are now the common single-oven default.
American recipes give Fahrenheit and almost always assume a conventional oven. 350 °F is the most common baking temperature in American recipes and corresponds to 177 °C, which is why British charts list it against 180 °C rather than an exact match.
Your oven is probably lying
Home oven thermostats commonly run some way off their dial setting, and the temperature swings as the element cycles on and off. An oven thermometer on the middle rack costs very little and tells you what is actually happening.
Preheating matters for the same reason. An oven that beeps when the air reaches temperature hasn't yet heated its walls and racks, which is where a lot of the cooking energy comes from for browning.
Common questions
What is 180 C in Fahrenheit and gas mark?
180 degrees Celsius is 356 Fahrenheit and gas mark 4. American recipes usually round this to 350 Fahrenheit.
Should I lower the temperature for a fan oven?
The usual convention is to reduce a conventional recipe temperature by about 20 degrees Celsius, or roughly 25 Fahrenheit. This is a widely reported cooking convention rather than a standards-body figure, so check your oven manual.
Should I reduce the temperature and the time?
No, apply one adjustment only. Reducing both at once overcorrects and is a common cause of undercooked centers.
Is there a formula for gas marks?
Yes, in Fahrenheit: degrees F equals 250 plus 25 times the gas mark, for marks 1 to 9. The scale looks irregular only in Celsius, because the Celsius figures printed in recipes are rounded conversions of the exact Fahrenheit values.
Related guides
Sources
- NIST Guide to the SI, Appendix B. National Institute of Standards and Technology. Source for the Celsius to Fahrenheit relationship, which is exact by definition.
- The 20 °C fan oven reduction is a widely reported cooking convention rather than a standards-body figure. It appears consistently across flour producers, recipe publishers and appliance guidance, including Cotswold Flour's oven conversion tables. Treat it as a rule of thumb and defer to your oven manual.
- Gas mark values follow the British scale as published in recipe and appliance references: 225 °F at gas mark 1/4, rising in exact 25 °F steps to 475 °F at gas mark 9. The Celsius figures in the column marked 'as printed' are the rounded values used by convention in recipes, not exact conversions.