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350°F = 177°C = gas mark 4. Fan oven? 157°C. The four languages of oven dials, one converter.
Recipes cross oceans; oven dials don't. American recipes speak Fahrenheit, European ones Celsius, British ones gas marks, and convection fans shift everything 20°C. This converter takes any Fahrenheit recipe temperature and returns conventional Celsius, fan-adjusted Celsius, gas mark, and the description — the complete translation.
Bakers with a British recipe use it: 350°F = 177°C = gas mark 4, and the fan oven knocks off 20°C — the one conversion Thanksgiving depends on.
Exactly 176.7°C, conventionally rounded to 175°C or 180°C depending on the cookbook — gas mark 4 on British ovens. It became the universal baking temperature because it is the sweet spot of the Maillard reaction: hot enough to brown and set structure, gentle enough to cook through before burning. Cookies, cakes, casseroles, and roasted chicken all default to it — a century of recipe writers converged on the same number because it forgives timing errors. The fan adjustment: moving air transfers heat faster, so convection ovens run 20°C (25°F) cooler for the same result — 350°F conventional becomes ~155–160°C fan. When a recipe doesn't specify, it assumes conventional.
Gas mark is the British dial system, roughly 25°F per mark starting from mark 1: mark 1 = 140°C/275°F, mark 2 = 150°C/300°F, mark 3 = 165°C/325°F, mark 4 = 180°C/350°F, mark 5 = 190°C/375°F, mark 6 = 200°C/400°F, mark 7 = 220°C/425°F, mark 8 = 230°C/450°F, mark 9 = 240°C/475°F. The descriptions pair with them: marks 1–2 "very slow/slow" (meringues, slow roasts), 3–4 "moderate" (most baking), 5–6 "moderately hot" (roast vegetables, pastry), 7–8 "hot" (pizza, bread crust), 9 "very hot" (initial searing heat). The marks exist because early gas ovens had no thermostats — the dial regulated gas flow, and mark numbers stuck around long after thermostats arrived.
Fan (convection) for anything that benefits from even, dry heat: roasted vegetables (crispier edges), multi-rack cookies (no rotating), puff pastry, and dehydrated anything. Conventional for delicate rise: soufflés, custards, cheesecakes, and quick breads — the fan's air movement can set the crust before the interior rises, producing lopsided cakes. The conversion rule: drop 20°C/25°F from the conventional temperature, and check 10–15% earlier — fan ovens also cook faster. Never fan a water bath. And the pro trick: start bread and pizza conventional-hot for oven spring, then switch to fan for even browning. If your oven only has fan mode, every American recipe needs the −25°F adjustment or the tops burn while centers stay raw.