Free Unit Conversion Data API (JSON)
One static JSON file with every unit on Scientific Converters: 145 units in 16 categories, each with its exact factor to the SI base unit, the defining expression, reference conditions and the source document. No key, no rate limit.
Licence and attribution
The data is licensed under CC BY 4.0. You may use it for any purpose, including commercially, if you credit Scientific Converters (scientificconverters.com) with a link to scientificconverters.com.
Unit data: <a href="https://scientificconverters.com/">Scientific Converters</a> (CC BY 4.0)How to convert with the data
- Each category has one base unit (pascal, metre, kilogram, kelvin …).
value_base = value × factor + offset(offset exists only for temperature scales).value_target = (value_base − offset_target) ÷ factor_target.factoris given to 20 significant figures;factorExpressionis the exact definition, e.g.0.45359237*9.80665/0.0254^2for psi.
Example (JavaScript)
const res = await fetch('https://scientificconverters.com/api/units.json');
const data = await res.json();
const pressure = data.categories.find((c) => c.id === 'pressure');
const u = (id) => pressure.units.find((x) => x.id === id);
// 125 Pa to inH2O
const valueBase = 125 * Number(u('pascal').factor);
console.log(valueBase / Number(u('inch-of-water').factor)); // 0.50182884…Fields
| Field | Meaning |
|---|---|
| id, name, plural, symbol, symbolAscii, aliases | Identifiers and names |
| factor, factorExpression | Multiplier to the category base unit (decimal string and exact expression) |
| offset, offsetExpression | Additive term to the base unit (temperature only) |
| exact | true if the factor is exact by definition |
| reference | Reference conditions (water and mercury columns, standard gas flow) |
| sources | Document title, URL and locator for each factor |
See also how we verify conversion factors and the changelog for data versions.