Converting between Fahrenheit and Celsius is arithmetic. The part that actually causes trouble is that a fan oven at the converted temperature cooks faster than the recipe intended, and most conversion charts stop before mentioning it.
The calculator below handles all three scales and adjusts between conventional and fan ovens in either direction. Our roundup of oven thermometers covers checking what your oven actually does.
Quick Answer
350F is about 180C or gas mark 4. For a fan or convection oven, reduce the conventional temperature by roughly 25F or 20C, which is about one gas mark, and start checking earlier than the stated time.
Key Points
- Fan ovens cook faster at the same dial setting, so the temperature comes down.
- The standard reduction is about 25F, 20C, or one gas mark.
- Time shifts as well as temperature, and the effect is largest on short bakes.
- Gas marks are coarser than the other scales, so conversions land between marks.
- Oven dials are frequently inaccurate, which a thermometer settles.
Common Temperatures Across All Three
| Fahrenheit | Celsius | Gas mark |
|---|---|---|
| 275F | 140C | 1 |
| 325F | 165C | 3 |
| 350F | 180C | 4 |
| 375F | 190C | 5 |
| 400F | 200C | 6 |
| 425F | 220C | 7 |
Why Fan Ovens Need Less Heat
A conventional oven heats by radiation from its elements and by air that circulates only because hot air rises.
A fan oven forces air across the food, which transfers heat considerably faster and more evenly to the surface.
The practical result is that the same dial setting delivers more cooking to the food, so the setting has to come down to match what the recipe intended.
Roughly 25F, or 20C, or one gas mark is the widely used adjustment, and it holds well enough for most home cooking.
Some ovens apply this automatically when fan mode is selected, which is worth checking in the manual before adjusting twice. Our comparison of air fryer versus oven covers a related case.
Time Moves Too
Faster heat transfer means a shorter bake
This holds even after lowering the temperature.
Short bakes shift proportionally the most
A few minutes off a twenty minute bake is a lot.
Check it early rather than trusting the clock
The stated time assumes the oven the recipe was written for.
Long roasts tolerate the shift better
The margin for error is considerably wider.
Gas Marks Are Coarser
Gas marks step in larger increments than degrees, so converted temperatures frequently land between two marks.
Rounding to the nearest is standard practice, and the resulting difference is usually smaller than the variation in the oven itself.
The scale is not linear across its range either. The gap between low marks represents a different number of degrees than the gap between high ones.
Gas marks appear mainly in British and Irish recipes, which is where most conversion questions originate in the first place.
Where a recipe gives only a gas mark and your oven has degrees, converting to Celsius first and then to Fahrenheit avoids compounding rounding. Our guide on setting up a home baking station covers the equipment side.
Your Oven Is Probably Not Accurate
All of this arithmetic assumes the oven reaches the temperature on its dial, and many do not.
Ovens drift out of calibration over time, and a discrepancy of a meaningful number of degrees is common rather than exceptional.
The thermostat also cycles, so the temperature oscillates around the setting rather than holding steady at it.
An inexpensive oven thermometer left inside settles the question, and it is the only way to know whether a conversion problem is actually a calibration problem.
Where an oven runs consistently off, adjusting the dial to compensate is simpler than replacing anything, and knowing the offset is more useful than a perfectly converted figure.
Position in the Oven Matters Too
A conventional oven is not the same temperature throughout, which is why rack position appears in recipes at all.
Heat rises, so the upper part of the cavity generally runs hotter than the lower, and the back is usually hotter than the door.
The middle rack is usually the default in most recipes because it sits furthest from both elements and represents the most average conditions available.
Fan ovens even this out considerably, which is one of their real advantages and part of why they suit baking multiple trays at once.
Rotating trays partway through is the standard fix in a conventional oven, and it matters more the further from center a tray sits.
Preheating Is Part of the Conversion
A converted temperature only means something once the oven has actually reached it.
Most ovens signal readiness before the cavity and its interior surfaces have fully stabilized, since the sensor responds to air temperature faster than the metal around it does.
Giving an oven longer than its indicator suggests is a common recommendation, particularly for baking where the initial burst of heat sets structure.
This matters more with a preheated surface like a stone or steel, which needs considerably longer than the air around it to come up to temperature.
Where Precision Actually Matters
Not everything cares about a twenty degree difference, and knowing which dishes do saves worry on the ones that do not.
Roasting is forgiving. Meat and vegetables tolerate a wide range, and the difference shows up as browning rather than failure.
Baking is the opposite. Cakes and pastries depend on structure setting at a particular rate, and a temperature that is off produces sunken centers or dry edges that are hard to diagnose afterward.
Bread sits in between, needing high heat but tolerating variation within it.
Custards and anything with eggs as structure are the least forgiving, since the margin between set and curdled is narrow. Our roundup of cake pans covers the other half of baking setup.
Convection Roast Versus Convection Bake
Ovens offering more than one fan mode add a step that catches people, since the modes behave differently.
Convection bake generally runs the fan with the standard heating elements, which is the mode the usual temperature reduction was written for.
Convection roast typically adds the top element and runs the fan harder, aiming for browning rather than even heat.
Applying a baking reduction while using a roast mode produces something browner and faster than intended, which is fine for a chicken and unhelpful for a cake.
Where a recipe just says convection, the bake mode is the safer assumption.
Common Mistakes to Avoid
Converting the temperature but not for the oven type
A correct Celsius figure in a fan oven still cooks faster than the recipe intended.
Adjusting for the fan twice over
Some ovens already compensate in fan mode. Lowering again puts you well below target.
Keeping to the stated time
Time shifts alongside temperature, and short bakes shift proportionally more.
Trusting the dial on the front
Ovens drift out of calibration. A thermometer distinguishes a conversion problem from a calibration one.
Recommended Reading
See our roundup of baking sheets, our roundup of air fryers, our note on why bakeware warps, and our guide on organizing your kitchen.
Oven Conversion FAQ
What is 350F in Celsius?
About 180C, or gas mark 4. The exact arithmetic gives 176.7C, which rounds to the nearest usable dial setting.
Do I lower the temperature for a fan oven?
Yes. Roughly 25F, 20C, or one gas mark below the conventional figure, since forced air transfers heat faster.
Does the cooking time change as well?
It does. Even after lowering the temperature, fan ovens generally finish sooner, and the difference is proportionally largest on short bakes.
What if my oven adjusts automatically?
Some do in fan mode. Check the manual, because lowering the temperature again puts you well below what the recipe intended.
Why do gas mark conversions look imprecise?
Gas marks step in larger increments than degrees, so converted figures land between marks. Rounding to the nearest is normal.
Is my oven accurate?
Frequently not. Ovens drift out of calibration and thermostats cycle around the setting. An oven thermometer is the only way to know.
Does this matter for everything I cook?
Roasting is forgiving. Baking is not, since structure depends on setting at a particular rate.
Which direction should I convert first?
From gas marks, convert to Celsius then to Fahrenheit. Going straight across compounds the rounding.
