Temperature Converter

You're reading a recipe from a UK food blog in Celsius, your oven only knows Fahrenheit, and the laboratory protocol you found uses Kelvin because that's how chemistry papers are written. Three scales, two arbitrary reference points, and one absolute scale that physicists insisted on — the math is fast but easy to flip if you're tired.

Water freezes at 0°C, 32°F, and 273.15 K, and boils at 100°C, 212°F, and 373.15 K. The Fahrenheit-to-Celsius conversion has that pesky 5/9 factor and a 32-degree offset, which is why mental conversions are off by a few degrees more often than not. Plug in the value, pick what you have, and read the rest.

The formulas: F = C × 9/5 + 32, and C = (F − 32) × 5/9. Kelvin to Celsius is just a 273.15 offset (K = C + 273.15) because Kelvin uses the same degree size as Celsius. Fahrenheit's 9/5 ratio comes from the original 1724 calibration where Daniel Fahrenheit set 0°F at the temperature of a brine ice mixture and 96°F at human body temperature; the scale was later anchored to water's freezing and boiling points, which landed on the awkward 32 and 212 numbers because that's what fell out of the calibration. Celsius (originally inverted, with 0 boiling and 100 freezing — Anders Celsius had his reasons) was flipped after his death and standardized on water's phase changes for simpler math.

A worked example: a recipe says 180°C. Multiply by 9/5: 180 × 9 / 5 = 324. Add 32: 356. So 180°C = 356°F, which is the standard "medium" oven temperature American recipes call 350°F. The 6-degree gap doesn't matter for baking because home ovens routinely fluctuate by 25°F regardless. Going the other way: a meat thermometer reading 165°F. Subtract 32: 133. Multiply by 5/9: 73.9°C. That's safe-poultry-cooked temperature in metric — useful if your sous-vide circulator wants Celsius input.

Where conversions get touchy is at the extremes. Cryogenics work in Kelvin because the Celsius value is large and negative (liquid nitrogen at 77 K = -196°C); kelvin keeps the numbers positive and readable. Astrophysics often uses kelvin for the same reason at the other extreme — the surface of the sun at 5,778 K reads more naturally than 5,505°C. And Rankine, the Fahrenheit-sized absolute scale, shows up in older American engineering work but is rare enough that this converter doesn't include it. If you need it, the conversion is: R = F + 459.67.