Fahrenheit to Celsius Cooking Converter

Oven temperature conversion is an affine transformation, not a simple scaling, because the Fahrenheit and Celsius scales differ in both zero point and degree size. There are 180 Fahrenheit degrees between water's freezing and boiling points against 100 Celsius degrees, giving the ratio 5/9, and freezing sits at 32 F rather than 0. Hence C equals F minus 32, times 5/9, and the reverse is F times 9/5 plus 32. The two scales cross at minus 40. Kelvin shares the Celsius degree but starts at absolute zero, so K equals C plus 273.15, and Rankine shares the Fahrenheit degree at F plus 459.67. British gas ovens use a third system, the gas mark, which is an index rather than a temperature: gas mark 1 is about 275 F or 140 degrees C, and each mark up adds roughly 25 F. Common baking settings run 325 to 425 F, or 163 to 218 degrees C, with 350 F equal to 177 degrees C and usually rounded to 180 in metric recipes. Sugar caramelizes from around 160 degrees C and Maillard browning becomes brisk above about 140 degrees C, which is why low ovens produce pale results regardless of time. USDA guidance specifies internal minimums rather than oven settings: 165 F or 74 degrees C for poultry, 160 F or 71 degrees C for ground meats, and 145 F or 63 degrees C with a three-minute rest for whole cuts. Rounded metric equivalents in recipes are approximate by up to 5 degrees C, and fan ovens usually need the setting reduced by about 20 degrees C.

Daniel Gabriel Fahrenheit, a German-born instrument maker working in Amsterdam, introduced his scale around 1724 after developing reliable mercury-in-glass thermometers. He fixed his zero using a freezing brine of water, ice and ammonium chloride and calibrated upper points from ice water and body temperature, which is why the freezing and boiling points of water landed on the awkward values 32 and 212. Anders Celsius, an astronomer at Uppsala University, presented his centigrade scale in 1742, originally inverted with 0 at boiling and 100 at freezing; it was reversed shortly after his death in 1744. The name Celsius replaced centigrade officially in 1948. William Thomson, later Lord Kelvin, proposed an absolute thermodynamic scale in 1848. Gas marks have a separate, commercial origin. Early gas ovens had no thermostat, and cooks judged heat by holding a hand inside or by how quickly paper browned, which is the source of oven descriptions like slow, moderate and hot in old recipes. Automatic gas oven thermostats arrived in the early twentieth century, and British manufacturers, notably Radiation Limited with its Regulo control introduced in the 1920s, marked the dial with numbered settings rather than degrees. Those numbers became the gas marks printed in British cookbooks for decades. Britain's metrication programme from the 1960s pushed published recipes toward Celsius, and modern British cookbooks typically print Celsius, fan Celsius, Fahrenheit and gas mark together, because all four systems remain in circulation.