Recipe in Celsius, oven in Fahrenheit — or a British cookbook that only says “gas mark 5”? Pick what the recipe gives you (°F, °C, fan °C or gas mark), type the number or tap a common setting, and you get the setting for your oven: Fahrenheit and Celsius rounded the way dials and recipes show them, the exact conversion, the fan / convection equivalent, the gas mark and the old-fashioned oven term (moderate, hot) with what that heat is usually used for. The oven temperature chart under the result highlights the row you are on.
How it works: °C = (°F − 32) × 5 ⁄ 9 and °F = °C × 9 ⁄ 5 + 32. Recipes round to the nearest 25 °F or 10 °C, so 350 °F is written as 180 °C even though the exact figure is 176.7 °C — a smaller gap than most ovens’ own error. Gas mark 1 is 275 °F and each mark adds 25 °F (gas mark ½ = 250 °F, ¼ = 225 °F). Fan and convection ovens cook faster, so UK recipes drop about 20 °C and US guidance drops 25 °F; check the food a few minutes early either way. Every result is an estimate — home ovens often run hot or cold, and an oven thermometer is the only way to know what yours really does.