Oven Temperature & Time Converter

The Complete Guide to Oven Temperature Conversion

Every cook eventually hits the same wall. A recipe from a British food writer says gas mark 6. An American blog says 375°F. A European cookbook says 190°C fan. A viral video says twenty minutes in the air fryer at 180. These are all attempts to describe roughly the same amount of cooking, expressed in four incompatible systems, and converting between them is not simply a matter of arithmetic — because two of those numbers describe a temperature and two of them describe a temperature plus an airflow condition that changes how fast heat actually reaches the food.

The converter above handles all four by normalising everything to a single reference point — a conventional static oven in Celsius — and then deriving the rest outward from there. That intermediate step is what most published conversion tables skip, and skipping it is why you sometimes see a fan-to-air-fryer conversion that is off by 40 degrees. Enter what your recipe says, tell the tool which kind of oven it assumed, and every other setting appears alongside the time each one requires.

Celsius to Fahrenheit: The Arithmetic

The formula itself is fixed: °F = (°C × 9/5) + 32, and in reverse, °C = (°F − 32) × 5/9. The 32 exists because the two scales put their zero points in different places — water freezes at 0°C and 32°F — and the 9/5 exists because a Fahrenheit degree is a smaller interval than a Celsius degree. There is a useful mental shortcut for oven work: double the Celsius figure and add 30. For 180°C that gives 390, against a true value of 356 — too far off for baking, but close enough to know whether you are in cake territory or pizza territory. For anything you actually care about, use the real formula or the table below.

In practice, recipe authors round. A recipe written in Fahrenheit at 350°F converts to 176.7°C, which every cookbook prints as 175°C or 180°C. Both are correct, because no domestic oven holds a temperature tightly enough for three degrees to matter — of which more below.

Why a Fan Oven Is Faster, Not Hotter

This is the single most misunderstood point in oven conversion, and it is worth being precise about. Set a conventional oven and a fan oven to the same 180°C and the air inside both really is at 180°C. The fan does not raise the temperature. What it does is destroy the boundary layer — the thin envelope of cooler, moisture-laden air that forms against the surface of anything you put in a still oven. That layer acts as insulation. Circulating air sweeps it away continuously, so heat transfers into the food faster at an identical air temperature.

This gives you a genuine choice, and it is one the calculator makes explicit. You can drop the temperature by 20°C and keep the recipe's stated time, which is the standard advice and the safer option for cakes and anything with a delicate crumb. Or you can keep the temperature and cut about a quarter of the time, which suits roasting, where you want aggressive browning. What you must not do is both — dropping the temperature and shortening the time is how you end up with a pale, underbaked centre, and it is the most common conversion error there is.

Where the Air Fryer Fits

An air fryer is a small convection oven with an unusually powerful fan, and understanding it that way removes most of the mystery. Two things follow from the small chamber. First, the food sits much closer to the heating element, so radiant heat is proportionally more significant than in a full-size oven. Second, the airspeed is far higher, which strips the boundary layer even more aggressively than a standard fan. The working correction is to drop roughly 25°C below the conventional temperature and cut the time by about a fifth.

Two caveats matter more than the numbers. Air fryers preheat in two or three minutes rather than fifteen, so a recipe's time may assume a warm-up you no longer have — check earlier than the converted figure suggests, not later. And the basket is small: crowding it defeats the entire mechanism, since air that cannot circulate cannot strip anything. Cook in batches with space between pieces, and expect your particular model to run five to ten degrees off its dial, as most do.

Gas Marks Are Steps, Not Degrees

The British gas mark scale is a numbered sequence rather than a continuous measurement, which makes conversion a matter of finding the nearest step rather than calculating an exact value. Each whole mark from 1 upward represents roughly a 25°F increment: mark 1 is about 275°F, mark 4 about 350°F, mark 9 about 475°F. Below mark 1 the scale drops to fractions — mark ½ and mark ¼ — for the very low temperatures used in meringues and long braises. There is no gas mark 10; mark 9 is the top of the domestic scale.

Because the marks are coarse, a Celsius target sometimes falls between two of them, and the calculator picks the nearest. Gas ovens have a second characteristic worth knowing: they produce water vapour as a by-product of combustion, so the cavity is slightly more humid than an electric oven. That extra moisture is mildly helpful for bread crust development and mildly unhelpful for anything you want bone dry, such as pavlova.

Your Oven Is Probably Not the Temperature It Claims

Before you fine-tune any conversion, it is worth knowing that domestic ovens routinely run 10–20°C away from their dial setting, and some are worse. The thermostat does not hold a steady temperature either — it cycles the element on and off, so the real internal temperature oscillates in a band around the target rather than sitting on it. An inexpensive oven thermometer left on the middle shelf for twenty minutes after the preheat light goes out will tell you your actual offset, and that single number is more valuable than any conversion table.

Hot spots are the related problem. Almost every oven is hotter at the back and near the element, which is why rotating trays halfway through a bake is standard advice rather than fussiness. A quick diagnostic: cover a rack with slices of white bread and toast them at 200°C for five minutes. The browning pattern maps your oven's geography, and you can position pans accordingly from then on.

Frequently Asked Questions