You find a beautiful bread recipe from a British blog. The instructions say "bake at 180°C, gas mark 4." Your oven in the United States is marked in Fahrenheit. If you guess — or worse, if you treat it as a simple multiply-by-two — you will either underbake a doughy loaf or turn the crust into a cinder. Oven temperature conversion is one of the few unit conversions where the offset matters as much as the scale, and getting it right is the difference between a bakery result and a science experiment gone wrong.
In this guide, we explain exactly how Celsius, Fahrenheit, and gas marks relate to one another, give you the precise formulas, and cover the practical adjustments — including convection ovens — that recipes rarely spell out.
1. Why Celsius and Fahrenheit Don't Convert Like Other Units
Most unit conversions are simple scaling: 1 inch is 2.54 centimeters, so 10 inches is exactly 10 × 2.54 centimeters. Temperature is different because the two scales use different zero points and different degree sizes:
- Water freezes at 0°C but 32°F.
- Water boils at 100°C but 212°F.
- A change of 1°C equals a change of 1.8°F (the scales are offset by 32 degrees and the Fahrenheit degree is 5/9 the size of the Celsius degree).
Because of the offset, multiplying is never correct. The exact formulas are:
°C = (°F − 32) × 5/9
The quick mental trick — double the Celsius temperature and add 30 — gives you a useful estimate for cooking conversations, but it is off by a few degrees at baking temperatures. For a 180°C recipe, doubling gives 360, plus 30 is 390°F; the exact answer is 356°F. Close enough to decide which oven rack to use, wrong enough to matter for delicate bakes.
2. The Standard Oven Temperature Table
In practice, nearly every recipe in the world uses one of a small set of "rounded" temperatures, and these are the values worth memorizing. This is the conversion table used across British, Australian, and American cookbooks:
| Fahrenheit | Celsius | Gas Mark | Common Use |
|---|---|---|---|
| 225°F | 110°C | ¼ | Very slow — meringues, slow-roasted meat |
| 250°F | 120°C | ½ | Slow — dried fruit, custards |
| 275°F | 135°C | 1 | Very low — cheesecake, brisket |
| 300°F | 150°C | 2 | Low — slow roasts, casseroles |
| 325°F | 160°C | 3 | Moderate-low — brownies, meatloaf |
| 350°F | 175–180°C | 4 | Moderate — cakes, cookies, most baking |
| 375°F | 190°C | 5 | Moderate-hot — pies, pastries, roasting |
| 400°F | 200°C | 6 | Hot — bread, roasting vegetables |
| 425°F | 220°C | 7 | Very hot — pizza, roasting poultry |
| 450°F | 230°C | 8 | Extremely hot — high-heat roasting |
| 475°F | 245°C | 9 | Max — broiling, Neapolitan-style pizza |
Notice the pattern in the table: gas marks step by one for every 25°F (roughly 14°C), which is why gas ovens and their recipes are so easy to convert between — just count marks. The exact conversions for any specific temperature are available in our celsius to fahrenheit and fahrenheit to celsius converters.
3. How Gas Marks Work
Gas marks, used in the UK, Ireland, and Commonwealth cookbooks, are a number assigned to each rung of a gas oven's dial, where mark 1 = 275°F (135°C) and each higher mark adds 25°F (about 14°C). The relationship to Celsius is roughly:
Gas mark 4 (350°F / 180°C) is the single most common baking temperature in British recipes, so if you memorize nothing else, memorize that one. For anything else, count marks from mark 1 at 275°F: mark 5 is 375°F, mark 6 is 400°F, and so on. Modern electric ovens in the UK often show both Celsius and gas marks on the same dial, which makes cross-referencing easy.
4. Convection (Fan) Ovens: The Adjustment Recipes Leave Out
A convection oven circulates hot air with a fan, cooking food faster and more evenly than a conventional (still-air) oven — so the same recipe needs less heat. The standard rule:
For a 350°F conventional recipe, set a convection oven to 325°F. In Celsius terms, that is roughly a 15–20°C reduction (many recipes simply round down to the nearest 10°C). Some newer ovens label this as "true convection" versus "convection bake" — true convection circulates more aggressively and may need the full 25°F drop, while a lighter convection-bake setting might need only 15°F.
Watch the food rather than the clock: convection also browns faster, so check baked goods a few minutes early on the first attempt with a new oven.
5. Common Mistakes and How to Avoid Them
- Multiplying instead of converting. "180 × 2 = 360" is wrong; the correct answer is 356°F. Always apply the +32 offset (or subtract it) — or use a converter.
- Confusing °C and °F symbols. A recipe asking for 200°F is a slow, gentle cook; 200°C is a hot oven. Misreading the symbol swings the temperature by 200 degrees in baking terms.
- Forgetting the oven is already hot. Preheating matters more at converted temperatures; a cold oven set to the right number still bakes like a cooler oven for the first 15 minutes.
- Converting mid-recipe. If a recipe lists multiple temperatures (e.g., "start at 425°F, reduce to 350°F"), convert both before you start so you are never doing arithmetic with hot pans in hand.
- Trusting the dial over an oven thermometer. Home ovens routinely drift 25–50°F from the dial setting. An $8 oven thermometer is the single best precision upgrade in baking.
6. What About Kelvin and Other Scales?
Baking never uses kelvin, but science does. The kelvin scale shares the Celsius degree size and simply starts at absolute zero (−273.15°C), so K = °C + 273.15. There is no offset complication because kelvin has no "degrees" — just kelvins. If you ever need it, our celsius to kelvin converter handles it, but for the oven, Celsius, Fahrenheit, and gas marks cover every recipe you will encounter.
Conclusion
Oven temperature conversion looks simple and punishes carelessness. Remember the three essentials: apply the offset (never just multiply), memorize the standard table (350°F = 180°C = gas mark 4), and drop 25°F when switching to a fan oven. Do those three things and any recipe — British, American, Australian, or French — will come out of your oven exactly as its author intended.