Celsius to Fahrenheit converter

Two scales built a generation apart

Daniel Fahrenheit proposed his scale in 1724, anchoring 0 degrees to the coldest temperature he could reliably make in his lab with a salt and ice mixture, and setting human body temperature at about 96 degrees, an estimate later refined to 98.6 with more accurate thermometers.

Anders Celsius introduced his own scale in 1742, originally with 0 as boiling and 100 as freezing, the reverse of how it is used today. The scale was flipped to its modern direction not long after his death in 1744.

Both scales stuck around for the same reason: whichever one a country's weather reports, cookbooks and thermostats used first tended to stay in daily use even after the metric system took over everything else, which is exactly what happened in the US.

Temperatures worth knowing in both scales

Estimating Fahrenheit without a calculator

Double the Celsius figure and add 30. It stays within a couple of degrees for most everyday weather: 5C doubles to 10, plus 30 is 40, close to the exact 41F. It drifts further off at higher temperatures, so treat it as a quick gut check, not a substitute for the exact formula.

The shortcut happens to land exactly right at 10C, where doubling and adding 30 gives 50, matching the real formula precisely. At very cold temperatures it drifts more: -20C doubles and adds 30 to give -10, well off the exact -4F.

Where each scale is used

Celsius is the standard for weather, cooking and science almost everywhere in the world, and the only scale most countries teach in school. Fahrenheit survives mainly in the US, where forecasts, oven dials and thermostats still default to it, which is why recipes and weather reports written for a US audience need converting for readers anywhere else.

Even scientists in the US report lab temperatures in Celsius or Kelvin, so Fahrenheit is really limited to weather, cooking and home comfort settings rather than technical work.