Unit Conversion API: One Endpoint, Ten Categories

Every product with international users eventually needs unit conversion, and hand-rolled conversion tables are where subtle bugs live (looking at you, temperature offsets).

One GET converts between any two compatible units across ten categories — pass a value, from, and to using short codes like km, mi, kg, lb, c, f. The category is inferred automatically.

Convert a value

curl -G "https://unit-converter26.p.rapidapi.com/convert" \
  -d "value=100" -d "from=km" -d "to=mi" \
  -H "X-RapidAPI-Key: YOUR_KEY" \
  -H "X-RapidAPI-Host: unit-converter26.p.rapidapi.com"

{
  "value": 100,
  "from": "km",
  "to": "mi",
  "category": "length",
  "result": 62.1371
}

Build dropdowns dynamically

GET /categories lists all ten categories, and GET /units returns every unit code within a category — so a converter UI can populate its selectors and validate input without hardcoding unit lists that drift out of sync with the backend.

The categories

Length, mass, temperature, volume, area, speed, data size, time, pressure, and energy. Temperature handles the offset conversions (Celsius/Fahrenheit/Kelvin) correctly — the classic source of DIY conversion bugs. Everything is pure math, stateless, and instant.