UnifyUnits Developers

GET /v1/substances Requires API key

List substances

Lists the substances with a sourced reference density, used by `POST /v1/substance/convert`: metals, polymers, woods, construction materials, liquids, and gases. Each entry includes its density in kg/m3, the conditions it applies to, and the source with the date it was checked. Available on every plan.

Prefer a language client when available: JavaScript / TypeScript, Python, or PHP (Laravel). Samples on this page stay raw HTTP so they match the OpenAPI contract.

Parameters

Name Type Required Description
category string No Filter by category: metal-alloy, polymer, wood, construction-solid, liquid, or gas

Possible errors

UNKNOWN_CATEGORY · UNAUTHORIZED · INVALID_API_KEY · RATE_LIMIT_EXCEEDED

All endpoints · Error reference

cURL
curl "https://api.unifyunits.com/v1/substances?category=liquid" \
  -H "Authorization: Bearer $UNIFYUNITS_API_KEY"

Response 200

json
{
  "data": [
    {
      "id": "ethanol",
      "name": "Ethanol (ethyl alcohol)",
      "category": "liquid",
      "density": { "value": "789.3", "unit": "kg-m3" },
      "conditions": "NIST radiation-calculation reference density; temperature and pressure not specified",
      "source": {
        "organization": "National Institute of Standards and Technology",
        "title": "STAR material composition: Ethyl alcohol",
        "url": "https://physics.nist.gov/cgi-bin/Star/compos.pl?matno=153",
        "accessed_date": "2026-09-13"
      }
    }
  ],
  "meta": { "count": 55 }
}