計算の仕組み
Everything is normalised to Celsius first. A Fahrenheit entry becomes (°F − 32) × 5/9, a Celsius entry passes straight through, and a Gas Mark entry is looked up in a fixed table where mark 1 is 140°C, 4 is 180°C and each step above adds 10°C to a maximum of 240°C at mark 9. The tool then converts back with °C × 9/5 + 32, picks whichever gas mark sits closest in Celsius, and labels the result with a description band from very cool up to searing.
The From selector decides how your number is read, and the eight presets from 200°F up to 500°F all switch it back to Fahrenheit. Oven type controls the headline figure while the separate Fan-forced line always reports your temperature minus 20°C, which is the number to use if your oven has a fan. The two reference tables below are static: gas mark equivalents on one, and safe or preferred internal meat temperatures on the other.
Fan compensation is a flat 20°C at every setting, so it is proportionally severe at low temperatures — a fifth off a 110°C dehydrate, but under a tenth off a 240°C roast. Note that 20°C is a 36°F difference, not the 40°F often quoted. Gas marks snap to the nearest whole entry, so intermediate temperatures round by up to 5°C, and nothing here corrects for altitude or for the fact that most domestic ovens run 10–15°C away from their dial.
よくある質問
What is gas mark 4 in Celsius and Fahrenheit? +
Gas mark 4 is 180°C, the most common baking temperature in British recipes. The chart pairs it with the everyday American 350°F, although the exact arithmetic conversion of 180°C is 356°F. The scale runs from mark 1 at 140°C in 10°C steps to mark 9 at 240°C.
How much should I lower the temperature for a fan oven? +
By 20°C, which the Fan-forced line calculates for you. In Fahrenheit that is a 36°F drop, not the 40°F frequently quoted. As an alternative to dropping the temperature, keep it as written and cut the cooking time by roughly a quarter.
Can I enter gas mark one-quarter or one-half? +
Not through the input box, which only accepts numbers and only matches whole marks 1 to 9. Read those two directly from the chart instead: gas mark one-quarter is 110°C or 225°F, and one-half is 120°C or 250°F.
What internal temperature should chicken reach? +
The doneness chart gives 165°F, or 74°C, as the safe minimum for chicken and turkey. Dark thigh meat is listed separately at 175°F, or 79°C, because the connective tissue in it needs the extra heat to break down and taste tender rather than rubbery.
Why does my food cook faster than the chart suggests? +
Dial settings are nominal. Domestic ovens commonly swing 10–15°C either side of the setpoint, and shelf position, tin colour and how full the oven is all change the effective heat. An oven thermometer on the middle shelf will tell you your own offset.
