Oven Temperature Conversion Guide: Fan, Conventional, Gas Mark and Celsius

Overview

Oven temperature conversion sounds simple, but it often causes confusion in real kitchens. A recipe might say 180C fan, while your cooker uses gas mark. Another might list 200C conventional, while your oven is fan-assisted and tends to run hot. For UK home cooks, this matters because a small temperature difference can change the texture of cakes, the colour of roast potatoes and the cooking time of tray bakes.

The quickest way to think about it is this: fan ovens usually cook slightly faster and more evenly than conventional ovens, so the fan setting is commonly around 20C lower than the equivalent conventional setting. Gas mark is simply another way of expressing oven heat, and many older British recipes still use it.

Here is a practical oven conversion chart UK cooks can return to whenever needed:

If you only remember one rule, make it this: when converting from conventional to fan, reduce by about 20C. When converting from fan to conventional, add about 20C. That will get you close enough for most savoury meals, easy baking recipes and weeknight dinner ideas.

Still, conversion is only the starting point. Ovens vary, shelf position matters, and some foods are more forgiving than others. That is why a cooking temperature guide should always be paired with a few sensible checks during cooking.

Core framework

Use this section as your working method. Rather than memorising lots of numbers, focus on a simple framework you can apply to almost any recipe.

1. Identify the temperature type first

Before changing anything, check what the recipe is actually giving you. Most recipes use one of these:

• Fan oven: often written as 160C fan, 180C fan or simply fan-assisted.
• Conventional oven: sometimes called standard oven, regular oven or non-fan oven.
• Gas mark: common in older UK cookbooks and handwritten family recipes.
• Fahrenheit: more common in US recipes, though some UK sites include it.

If the recipe says only “preheat oven to 180C” and gives no other clue, assume it may mean conventional unless the source clearly states otherwise. Many modern UK recipes now specify fan temperatures, but not all do, so it is worth checking the notes or recipe introduction.

2. Make the basic conversion

For most recipes, use these everyday rules:

• Conventional to fan: subtract 20C
• Fan to conventional: add 20C
• Gas mark 4: 180C conventional / 160C fan
• Gas mark 6: 200C conventional / 180C fan

These are not rigid scientific laws for every appliance, but they are reliable kitchen rules that work well for common home cooking.

3. Decide whether the recipe needs only a temperature change or a time check too

Temperature conversion is not always enough on its own. Some foods are forgiving, while others are more sensitive.

Usually straightforward:

• Roast vegetables
• Tray bakes
• Sausages
• Chicken pieces
• Frozen oven foods
• Many one pot meals finished in the oven

Needs a closer eye:

• Sponge cakes
• Cheesecakes
• Meringues
• Choux pastry
• Rich fruit cakes
• Custard-based dishes

For these more delicate recipes, treat the converted temperature as your starting point, then check a little before the stated cooking time ends.

4. Think about what the heat is meant to do

The best fan oven conversion is not always just about matching numbers. It also helps to understand the purpose of the oven temperature.

• Low heat is usually used to dry, gently set or slowly cook.
• Moderate heat is used for most cakes, biscuits and everyday roasting.
• High heat is used for crisp edges, puff pastry lift, pizza bases and quick browning.

If a dish needs a strong initial blast of heat, such as roast potatoes or puff pastry, converting the number correctly matters, but so does preheating the oven fully. If a dish needs steady, gentle cooking, such as baked cheesecake, avoiding excess heat is often more important than landing on an exact number.

5. Learn your own oven

No oven conversion chart can fully replace experience with your actual cooker. Some ovens run hotter than the dial suggests. Others have cool spots or brown more heavily at the back. If your cakes always colour too fast, your oven may be hot. If roast vegetables take much longer than expected, it may run cool.

A simple oven thermometer can help if you bake often. Even without one, keeping brief notes on a few regular dishes is useful. For example:

• Victoria sponge: better at 150C fan than 160C fan
• Roast potatoes: best on top shelf at 200C fan
• Lasagne: covers well at 170C fan, uncovers for final 15 minutes

That kind of record turns a generic cooking temperature guide into a personal reference that is far more useful over time.

Practical examples

These examples show how oven temperature conversion works in ordinary cooking, not just in theory.

Example 1: A cake recipe says 180C conventional

Your oven is fan-assisted. The simplest fan oven conversion is to drop the temperature to 160C fan. Start checking the cake 5 to 10 minutes before the end of the stated baking time, especially if your oven tends to run warm.

Signs it is ready may include:

• A springy centre
• Slightly shrinking from the tin edges
• A skewer coming out clean or with a few crumbs, depending on the cake type

Example 2: An older British recipe says gas mark 6

Gas mark 6 converts to 200C conventional or 180C fan. This is a common temperature for roasting chicken pieces, baking pastry-topped pies and making many tray bake recipes.

If you are cooking a family dinner and the recipe feels broad rather than precise, this conversion is usually all you need. If you are following a specific bake, watch the final stage more carefully.

Example 3: A roast potato method says 220C conventional

For a fan oven, set it to about 200C fan. Because roast potatoes rely on high heat for crisp edges, make sure the oven and roasting tray are fully preheated before the potatoes go in. In recipes like this, poor preheating causes more problems than tiny conversion differences.

For more roast timing help, see Sunday Roast Timings Guide: How Long to Cook Beef, Chicken, Lamb and Pork.

Example 4: A casserole recipe says 160C fan but you have gas mark

160C fan is roughly equivalent to 180C conventional or gas mark 4. For long, covered cooking, being exact matters less than for baking. If the dish is still firm or the meat is not tender by the end, extend the time rather than raising the heat aggressively.

If you enjoy set-and-forget meals, you may also like Slow Cooker Recipes UK: The Best Set-and-Forget Meals for Every Season.

Example 5: A US recipe says 350F

350F is about 180C conventional or 160C fan, which is one of the most common baking temperatures. This is useful for cookies, sponge cakes and many simple dessert recipes. If the recipe also uses cup measurements, convert those separately rather than assuming the whole recipe will behave exactly like a UK one.

Example 6: Reheating a batch-cooked pasta bake

For reheating rather than cooking from raw, exact conversion is less critical. A moderate oven, around 180C conventional / 160C fan / gas mark 4, works well for many freezer meals and batch-cooked dishes. Cover at first to prevent the top drying out, then uncover near the end if you want colour.

For more make-ahead ideas, visit Batch Cooking Recipes for the Freezer: Meals That Reheat Well.

Example 7: Cooking an easy tray bake dinner

Tray bakes are among the most forgiving formats for temperature adjustments, which is one reason they work so well for busy households and student meal ideas. If a recipe says 200C conventional, use 180C fan and check halfway through. Rotate the tray if one side browns faster.

For more one-tin options, see Easy Tray Bake Dinners: One-Tin Recipes for Less Washing Up.

Quick reference for popular temperatures

• 160C fan = 180C conventional = gas mark 4
• 170C fan = 190C conventional = gas mark 5
• 180C fan = 200C conventional = gas mark 6
• 200C fan = 220C conventional = gas mark 7

These are the temperatures many home cooks use most often for easy dinner recipes, family meal ideas, baking basics and everyday British cooking.

Common mistakes

Most oven problems come from a few repeat errors. If a recipe has not worked, the issue is often one of these rather than the recipe itself.

1. Converting the temperature but not considering the cooking time

Fan ovens circulate heat differently. Even with the correct temperature conversion, some foods may finish sooner. Start checking early rather than assuming the original timing will always hold.

2. Trusting the dial more than the food

The recipe can guide you, but the food gives the final answer. Cakes should look set. Chicken should be cooked through. Roasted vegetables should be tender and browned. If the food is not ready, keep cooking. If it is colouring too quickly, lower the heat slightly or cover it.

3. Opening the oven too often

Checking matters, but repeated door opening drops heat and can affect baking, especially for cakes and pastries. Wait until the food has mostly set before checking unless you can see a problem through the glass.

4. Ignoring shelf position

The same temperature can behave differently depending on where the dish sits. Top shelves tend to brown faster. Middle shelves usually suit cakes and general baking. Lower shelves often work well for larger dishes that need steady heat. If the top browns before the centre cooks, move the dish down or cover loosely with foil.

5. Skipping the preheat

This is one of the biggest causes of uneven results. Baking, roasting potatoes, pastries and pizzas all benefit from a fully heated oven. Starting in a cool oven can flatten pastry, delay browning and throw off cooking times.

6. Assuming fan means better for every recipe

Fan ovens are helpful and efficient, but some delicate bakes can dry or colour too fast if the heat is too aggressive. If a recipe repeatedly overbakes at the converted fan temperature, try dropping it by another 10C and extending the time slightly.

7. Using an old family recipe without checking the wording

Many classic UK recipes use gas mark or assume a conventional oven. If you are working from older handwritten notes for easy British recipes, convert carefully before starting rather than making a rushed guess halfway through.

If you enjoy traditional dishes, you might also like Easy British Recipes: Classic UK Dishes to Cook at Home.

When to revisit

This guide is worth revisiting whenever your kitchen setup changes or the recipe format changes. Oven conversion is not a one-time lesson; it is a reference you use whenever the inputs are different.

Come back to this chart and framework when:

• You move house and start using a new oven
• You switch from gas to electric, or from conventional to fan-assisted
• You start baking more often and want more consistent results
• You use older British cookbooks with gas mark settings
• You try international recipes with Fahrenheit temperatures
• You notice your usual dishes are browning too quickly or too slowly
• You add new appliances such as an air fryer and want to compare heat levels sensibly

If you cook across different appliances, keep a short note on what works for your favourite foods. For example, note the oven setting you prefer for chicken thighs, frozen chips, tray bakes or brownies. A personal reference is often more useful than a giant chart.

A practical way to use this guide is to save or print the temperature table, then add your own notes underneath:

• Best shelf for cakes
• Whether your oven runs hot or cool
• Which dishes need an early check
• Whether you prefer fan or conventional for certain bakes

That makes this a living kitchen reference rather than a page you read once and forget.

If your cooking routine includes air fryer meals or quick midweek dinners, it is also useful to build a wider conversion habit around timing and texture, not just temperature. These related guides can help:

• Best Air Fryer Recipes UK: The Everyday Favourites to Make on Repeat
• Student Meal Ideas: Cheap, Easy Recipes for One or Two
• What to Cook Tonight: 101 Easy Dinner Ideas for Busy UK Weeknights

To make this guide practical straight away, here is the shortest version to remember:

1. Check whether the recipe is fan, conventional, gas mark or Fahrenheit.
2. If converting between conventional and fan, change by about 20C.
3. Preheat fully.
4. Use the middle shelf unless the recipe says otherwise.
5. Check slightly early for cakes and delicate bakes.
6. Trust the look and texture of the food, not just the timer.

Once you get used to that rhythm, oven temperature conversion becomes less about maths and more about confidence. You will be able to switch between recipes, cookers and formats without second-guessing every number, which is exactly what a good kitchen reference should help you do.