convert
Units, in both directions
Length, mass, temperature and everything that follows. Pick any two units of a dimension; the engine composes the conversion through a base chosen for numerical stability.
definition only · zero code
Unit converters · part of every tool here
Convert anything. Every factor traced to its source.
Most converters ask you to trust a number nobody checked. Ours are transcribed from NIST SP 811 and verified against exact rational arithmetic on every build — and they run entirely in your browser.
°C = K − 273.15
NIST SP 811 (2008), Appendix B.8 — kelvin (K) to degree Celsius (°C): t/°C = T/K − 273.15
One engine, three kinds of tool
A converter, a calculator and a generator are the same thing: a function. That is why adding the hundredth tool costs one file of data, not one more application.
calculate
Formulas worth checking
A calculator is a function with a nicer face. The same definition carries its formula, its source and the values it must reproduce.
definition + interior
generate
Anything a function can describe
Colors, gradients, identifiers, passwords. If the output can be derived from the input, it belongs here — and it still runs on your machine.
definition + interior + logic
A converter that is wrong is worse than no converter
One bad factor costs the trust of the whole site, so a tool without passing tests does not get built. Reference values are transcribed from the standard — never produced by our own code, because code that checks itself proves nothing.
- Factors transcribed from NIST SP 811 Appendix B, with the citation kept next to the number
- Every unit offered in the dropdown must have a reference value, or the build fails
- Round trips, boundary values and exact rational arithmetic checked on each build
- The worst measured error is 2.2e-16 — the limit of double precision, not a compromise
- Temperature converts through Celsius, because routing via kelvin loses digits at 0 °C
kelvin-to-celsius.ts — the whole tool
from: 'km',
to: 'mi',
references: [{
from: 'mi', to: 'km',
input: 1, expected: 1.609344,
source: nist('mile (mi) to kilometer (km)', true),
}],Kelvin to Celsius at a glance
People search for a number, not a unit pair. This table answers the common ones on the page itself.
| kelvins | degrees Celsius |
|---|---|
| 0 | -273.15 |
| 100 | -173.15 |
| 173.15 | -100 |
| 233.15 | -40 |
| 253.15 | -20 |
| 273.15 | 0 |
| 293.15 | 20 |
| 298.15 | 25 |
| 310.15 | 37 |
| 373.15 | 100 |
| 500 | 226.85 |
| 1,000 | 726.85 |