Recipes, guides and kitchen know-how. Mostly useful, occasionally silly.
Oven Temperature Conversion - Fan, Gas Mark and Fahrenheit on One Chart (and Why Your Oven Is Lying)
One chart for conventional, fan, gas mark and Fahrenheit. Knock 20C off for a fan oven, and check what your oven is really doing before you blame the recipe.
For a fan oven, take 20C off the conventional temperature. Gas mark 4 is 180C (160C fan, 350F), gas mark 6 is 200C (180C fan, 400F) and gas mark 7 is 220C (200C fan, 425F). The full chart is below.
That's the oven temperature conversion most recipes forget to give you. Usually while you're standing there with the oven door open and flour on your phone.
Every recipe in Britain is written for a different oven. Gran's book says gas mark 5. The internet says 375F. The packet says 190C. Your oven says "fan" and a picture of a propeller.
Nobody agrees on anything. It's like a family meeting about where to go on holiday.
So here's one chart for all four, the reason fan ovens need less heat, and how to check whether your oven is telling you the truth. Spoiler: it probably isn't.
Aaron tested ours. He was very excited. He had a laser.
Why is it called gas mark?
Gas marks come from the Regulo, a numbered oven thermostat that a Birmingham company, Radiation Ltd, started fitting as standard to its gas cookers in 1923.
Before that, you guessed. Hand in the oven, count to ten, hope. Health and safety had not yet been invented.
The numbers stuck so hard that recipes still use them a hundred years on, even for electric ovens that have never seen a gas pipe. Grace's Guide to British Industrial History has the company's story, and the Science Museum has an original Regulo, sliced open so you can see its insides. Aaron wants to visit. Aaron wants to touch it. Aaron is not allowed to touch it.
Oven temperature conversion chart
Use the conventional column for an oven without a fan, the fan column for a fan oven, and gas or Fahrenheit if that's what the recipe gives you.
| Gas mark | Conventional | Fan | Fahrenheit | What it's for |
|---|---|---|---|---|
| ¼ | 110C | 90C | 225F | Drying meringues |
| ½ | 120C | 100C | 250F | Very slow |
| 1 | 140C | 120C | 275F | Slow cooking, rich fruit cake |
| 2 | 150C | 130C | 300F | Slow |
| 3 | 170C | 150C | 325F | Moderately slow, biscuits |
| 4 | 180C | 160C | 350F | Moderate - most cakes |
| 5 | 190C | 170C | 375F | Moderately hot, crumbles |
| 6 | 200C | 180C | 400F | Hot - roasting |
| 7 | 220C | 200C | 425F | Very hot - Yorkshires, bread |
| 8 | 230C | 210C | 450F | Very hot - pizza |
| 9 | 240C | 220C | 475F | As hot as most ovens go |
Different charts disagree by 10C here and there, especially at gas mark 3, which you'll see listed as 160C or 170C. The numbers are a starting point, not a law. Eesha disagrees. Eesha says all numbers are law.
Want it on the fridge? Here's the same chart as one picture you can save, print or pin.
How to convert Celsius to Fahrenheit (and back)
To turn Celsius into Fahrenheit, multiply by 9, divide by 5 and add 32. To go back, take off 32, multiply by 5 and divide by 9.
- 180C: 180 x 9 = 1,620. Divide by 5 = 324. Add 32 = 356F, which recipes round to 350F
- 425F: 425 - 32 = 393. x 5 = 1,965. Divide by 9 = 218C, which recipes round to 220C
- Rough and ready: double the Celsius and add 30. It's close enough at cake temperatures and wrong at everything else
American recipes are always Fahrenheit and almost never say whether it's fan. Assume they mean conventional, then knock off 20C if your oven has a fan. Americans call a fan oven a "convection oven". It sounds like a conference. It isn't.
Why do recipes round the numbers? Because most oven dials only go up in steps of 10C or 25F, and a few degrees either way makes no real difference to a cake. That's why 356F becomes 350F and 218C becomes 220C on every chart you'll ever see. Precision is for chemists. And Aaron.
Isaac did all of those in his head while I was finding a calculator. I found it eventually. It was in the fridge. Don't ask.
Fan oven conversion: take off 20C
A fan oven cooks hotter than its dial suggests, so set it about 20C lower than a conventional recipe says.
The fan blows hot air round the food instead of letting it sit there, and moving air passes heat on faster. Same reason a breeze feels colder on a cold day. It's not colder. It's just more enthusiastic.
Nigella's site gives the same 20C rule and says to check your oven's manual, because some models already adjust for you. Her answer to the fan oven question also says to check food a little early until you know your oven. That's the best advice in this whole post.
Gas mark conversion in plain English
Each gas mark from 1 to 9 is roughly 10 to 15C hotter than the one before, with gas mark 4 at 180C in the middle.
- Gas ¼ to 2 (110C to 150C): low and slow. Meringues, slow-cooked stews, rich fruit cakes
- Gas 3 to 5 (170C to 190C): the middle. Most cakes, biscuits and crumbles live here
- Gas 6 to 7 (200C to 220C): hot. Roast potatoes, roast chicken, Yorkshire puddings
- Gas 8 to 9 (230C to 240C): as hot as it goes. Pizza, flatbreads, and anything you want blistered
Old recipes sometimes just say "a moderate oven" or "a hot oven". Moderate is gas 4 (180C), moderately hot is gas 5 to 6, and hot is gas 7. "A cool oven" is what my oven becomes the moment the door opens.
Gas ovens also heat unevenly by design. The top shelf runs hotter than the middle and the bottom is cooler, which is why old recipes say things like "top shelf, gas 6". Electric fan ovens are much more even, so you can usually ignore shelf advice written for gas.
Gran knew all this without a chart. Gran also knew where everything in the house was. Gran was a different breed.
Is your oven lying? How to check
Most home ovens run a little hot or cold, so check yours: heat it to 180C for 20 minutes, then point an infrared thermometer at a metal tray on the middle shelf.
- Put an empty, dark metal tray on the middle shelf and heat the oven to 180C (160C fan). Wait 20 minutes after the light goes off, so the walls catch up.
- Open the door, aim a point-and-shoot infrared thermometer at the middle of the tray and read it straight away. Then check the back, the front and each side.
- Off by more than 10C? Adjust your dial by that much every time. All over the place? You've found your hot spots.
Ours read 196C at the back and 171C at the front. Aaron wrote it down. Then laminated it. Then stuck it on the oven.
Which temperature for what?
Bakes that rise need steady, moderate heat; things you want crisp need high heat; and anything delicate needs low heat for longer.
- Low (100C to 120C fan): meringues that need a low, slow oven and a lot of patience
- Middle (160C to 170C fan): sponges, brownies, biscuits
- Hot (180C to 200C fan): roasts, roast potatoes and puddings that need a properly roaring oven to climb
- Flat out (220C fan and up): pizza and bread - preheat the tray or stone too
Cooking several things at once? Planning one oven around six different dishes is exactly what our Christmas timer does. And for meat, check the food, not the oven - a probe that goes in the joint itself tells you when it's done. The oven only tells you how it feels. The probe tells you the truth.
Converting any recipe takes three questions:
- What does the recipe give you? Gas mark, Celsius or Fahrenheit. Find it on the chart.
- Does it say fan? If it gives one Celsius number and doesn't say, it almost always means conventional.
- Does your oven have a fan on? Then read across to the fan column. If not, use conventional.
Three questions. Ayden still got it wrong. He's an actor. He improvised.
If it goes wrong
Burnt outside, raw inside? Too hot - usually a conventional temperature in a fan oven.
Fix: Take 20C off for fan, and cover the top with foil if it's browning too fast. Charcoal is a colour, not a flavour.
Pale and taking forever? Too cool, or a fan temperature in a conventional oven.
Fix: Check which column you used and test the oven with the tray method above. Pale is just undercooked with good manners.
Cake sank in the middle? Oven too hot, so it rose fast and collapsed - or the door opened too early.
Fix: Lower it by 10C and keep the door shut for the first two-thirds of the time. A sunken sponge is still a sponge. It's just had a long day.
One side done, one side not? Hot spots - every oven has them.
Fix: Turn the tray round two-thirds of the way through. Erin calls it a royal rotation. Nobody argues.
Oven temperature questions people actually ask
What is 350F in gas mark? Gas mark 4. That's 180C in a conventional oven or 160C fan.
What is gas mark 4 in fan oven terms? 160C. The conventional equivalent is 180C.
What is 200C fan in a normal oven? 220C, or gas mark 7. Go the other way and 200C in a normal oven is 180C fan.
Does a fan oven cook faster? Usually, yes - even at the lower temperature. Check 5 to 10 minutes early the first few times. Your oven and you are still getting to know each other.
Should I use the top or bottom shelf? The middle, unless the recipe says otherwise. In a conventional oven the top is hottest. In a fan oven it's more even, which is the whole point of the fan.
Why does my recipe say "preheat"? Because a cold oven heats from the bottom element first and cooks unevenly. Wait until it's properly hot. The light going off is a suggestion. Give it ten more minutes.
What is 180C fan in gas mark? Gas mark 6. A fan setting of 180C does the same job as 200C conventional, which is gas 6.
What do the oven symbols mean? A fan inside a circle is a true fan oven - use the fan column. A fan with a line at the top and bottom is fan plus top and bottom heat, also fan column. Two lines, top and bottom, with no fan is conventional. A single zigzag line at the top is the grill. The snowflake is defrost. It is not a cold oven. Aaron checked.
What temperature is a hot oven? Gas mark 7, or 220C (200C fan). A very hot oven is gas 8 to 9, 230C to 240C.
Can I cook two things that need different temperatures? Usually, if they're within about 20C of each other. Pick the middle, put the one that wants more heat higher up, and check both early. This is how every Christmas dinner in Britain is made. And every argument.
Does an air fryer use the same temperatures? Not quite. Air fryers are small, powerful fan ovens, so many guides suggest starting about 20C lower than a conventional recipe and checking early. Follow your air fryer's own booklet first.
That's it. Take 20C off for fan, find your gas mark on the chart, and check your oven before you blame the recipe.
Aaron would like you to know he has now tested every oven in the family. Nobody asked him to. Several people asked him to stop.
Now go and turn the heat up. Or down. Check the chart.
