Temperature Converter
Enter a temperature, pick the units, and get an instant, correct conversion — plus the same value shown in all three scales at once. Nothing you type ever leaves your browser.
Same value in all three units
Why this page defaults from Fahrenheit
Both scales stay fully selectable in the dropdowns above — this is just the starting pair. Fahrenheit is the scale used in everyday US weather reports and home thermostats, so that's the default "from" unit here; readers who want Celsius→Fahrenheit or any other pairing can just change the dropdowns, and the result updates instantly either way.
Worked example
The three fixed points worth memorizing: water freezes at 0°C = 32°F = 273.15 K, water boils at 100°C = 212°F = 373.15 K, and the two scales
cross at −40°C = −40°F = 233.15 K. Try entering -40 with Celsius as the "from" unit and Fahrenheit
as the "to" unit above — the result comes back as exactly -40, which is the standard way this crossover point
gets verified.
Frequently asked questions
What formulas does this tool actually use?
The standard ones, applied directly: F = C × 9/5 + 32 and C = (F − 32) × 5/9 for Celsius↔Fahrenheit, and K = C + 273.15 and C = K − 273.15 for Celsius↔Kelvin. Fahrenheit↔Kelvin isn't a single textbook formula — this tool composes it by converting through Celsius as a pivot, which is also how the conversion is normally taught.
Why do Celsius and Fahrenheit meet at −40°?
Because the two formulas F = C×9/5+32 and C = (F−32)×5/9 are inverses of each other, and −40 happens to be the fixed point where they agree: −40°C converts to exactly −40°F. It's not a coincidence you need to memorize a table for — plug −40 into either formula and you get −40 back on the other scale.
Why can't Kelvin go below zero?
0 K (−273.15°C, −459.67°F) is absolute zero — the theoretical point where atoms have the least possible thermal motion. The Kelvin scale is defined to start there, so a negative Kelvin value doesn't correspond to any real temperature. This tool checks for that and shows a warning instead of quietly displaying an impossible number.
Is my input sent anywhere?
No. The conversion is plain arithmetic that runs in your browser — nothing you type is sent to a server, stored, or logged. That's true for every tool on this site.