Celsius vs Fahrenheit — same metric, different zero
Both measure hot/cold; one is taught in school everywhere, the other used in the US for daily life.
°F = °C × 9/5 + 32 — every country except the US uses °C
°C = (°F − 32) × 5/9 — US weather and cooking only
Celsius and Fahrenheit are the two scales taught in school — and they differ in three ways:
1. Zero point. Water freezes at 0 °C and 32 °F. The scale factor (which I'll come back to in a moment) plus this offset together make the relationship what it is. 2. Scale factor. A degree Celsius is bigger than a degree Fahrenheit by 1.8×. 100 °C spans water-ice to water-boil; 180 °F spans the same. That's the 9/5. 3. Magnitude. A comfortable room is 20–22 °C = 68–72 °F. A fever is 38 °C = 100.4 °F. A cold snowy day in Chicago is −10 °C = 14 °F.
Practical recommendation: - For weather in the US, learn Fahrenheit. - For weather everywhere else, Celsius. - For cooking, both work but US recipes give oven temperatures in °F (350 °F, 400 °F) and European ones in °C (180 °C, 200 °C). Double-check your oven's knob. - For science, Kelvin is the proper choice.
A few conversion shortcuts to memorize: - 0 °C = 32 °F - 100 °C = 212 °F - 20 °C = 68 °F - 30 °C = 86 °F - 40 °C = 104 °F
The site does the arithmetic to 6 decimal places.
Frequently Asked Questions
Which should I use?
Use Celsius for weather outside the US, in scientific and engineering contexts, and in most international cooking.
When is the alternative better?
Use Fahrenheit for US weather, cooking, and US medical thermometers.
How is the conversion calculated?
Every conversion is a single factor (or an affine formula). The math is identical either direction; the difference is context.