Converting oven temperatures and gas marks
Three systems describe the same oven heat: Fahrenheit, Celsius, and the UK gas mark. A recipe written in one and an oven that speaks another is a daily annoyance for anyone cooking from international cookbooks. This converter takes the one number you have and fills in the other two — tap which you know, type it, and read the rest.
Fahrenheit and Celsius are linked by the standard formula, °C = (°F − 32) × 5 ÷ 9, and the reverse, °F = °C × 9 ÷ 5 + 32. The two best-known kitchen anchors are 350°F = 177°C (usually rounded to 180°C, the all-purpose 'moderate' oven) and 400°F = 204°C. Because of the 32-degree offset, you can't simply scale a temperature the way you'd scale a quantity — every conversion runs through that formula.
Gas marks are the British dial, numbered 1 to 9, and they follow a tidy linear rule: °F = 250 + 25 × mark. Gas mark 4 lands on 350°F, gas mark 6 on 400°F, and each step up adds 25°F. Going the other way, mark = (°F − 250) ÷ 25. This calculator uses exactly that formula, so any temperature in range resolves to a gas mark and back without you memorizing the chart.
A caveat that matters more than the arithmetic: ovens lie. Most home ovens drift 15–25°F from their dial, and they run hotter near the top and the back. For forgiving dishes — a tray of roasted vegetables — the converted number is plenty. For anything where a few degrees decides the outcome, like bread or soufflés, hang a cheap oven thermometer inside and trust that over the dial.
Worked example
A British baking book says 'gas mark 6' and your oven only reads Fahrenheit and Celsius.
- °F = 250 + 25 × mark = 250 + 25 × 6 = 400°F
- °C = (400 − 32) × 5 ÷ 9 ≈ 204°C
→ Gas mark 6 = 400°F ≈ 204°C. Set the dial to 200°C, the nearest common mark.