Temperature Converter

How to use it

Temperature doesn't convert like the other categories on this page, because Celsius, Fahrenheit, and Kelvin don't share a common zero. Multiplying a Celsius value by a single factor would only work if 0°C meant 'no temperature,' the way 0 meters means no distance — but 0°C is just the freezing point of water, an arbitrary reference, not an absence of heat. So every conversion here uses a formula with both a multiplication and an addition (an offset), not just a ratio. To convert Celsius to Fahrenheit: °F = °C × 9/5 + 32. Water's freezing point, 0°C, becomes 32°F; its boiling point, 100°C, becomes 212°F — a 100-degree Celsius span equals a 180-degree Fahrenheit span, which is where the 9/5 comes from (180/100 = 9/5). Going the other way: °C = (°F − 32) × 5/9. A hot summer day of 86°F converts to (86 − 32) × 5/9 = 30°C. Kelvin is simpler by comparison: K = °C + 273.15, no multiplication needed, just a shift. Kelvin is the SI base unit for temperature, and it's built so that 0 K is absolute zero — the coldest physically possible temperature, where atoms have minimum thermal motion, equal to −273.15°C. Because Kelvin can never go below zero, it's the scale scientists use for anything involving thermodynamics, gas laws, or astrophysics, where negative numbers would be meaningless. A quick sanity check for any temperature conversion: room temperature is about 20-22°C, 68-72°F, or 293-295 K. If your converted result is wildly outside that range for an everyday temperature, double-check which direction you converted.

Frequently asked questions

Why isn't 0°F equal to 0°C?

Because the two scales use different zero points and different-sized degrees. 0°C is water's freezing point; 0°F comes from a different historical reference (roughly the coldest temperature Fahrenheit could reproduce with a brine mixture in 1724). The scales only agree at one single point, −40°, where −40°C equals −40°F exactly.

Why does Kelvin never use the degree symbol (°)?

Kelvin measures an absolute quantity from true zero, like counting a distance from a starting line rather than measuring how far above an arbitrary reference point you are. By SI convention it's written as '300 K,' not '300°K,' the same way you'd write '5 meters,' not '5°meters.'

What is absolute zero and why can't you go below it?

Absolute zero is −273.15°C (0 K), the temperature at which atoms hold the minimum possible thermal energy. It's a physical floor, not just a low number — there's no such thing as 'colder than no motion at all,' which is why Kelvin values are never negative.

How do I quickly estimate Celsius to Fahrenheit in my head?

Double the Celsius value and add 30 — it's close enough for weather chat, though not exact. 20°C doubled is 40, plus 30 is 70°F (the real answer is 68°F). For anything precise, like a recipe or a medical reading, use the exact formula instead of the shortcut.