---
title: "UnitConversion"
description: "An exact conversion between two units of the same kind."
url: "https://opsinjs.pensievelabs.org/reference/api/UnitConversion"
source: "https://opsinjs.pensievelabs.org/reference/api/UnitConversion.md"
section: "Reference"
kind: "reference"
---

> Elements written as `<PascalCase … />` below are opsinjs documentation
> components. Their attributes are the content: the values they render are
> generated from `tokens/*.json` and `registry/catalogue.ts` and are
> published separately at https://opsinjs.pensievelabs.org/r/index.json and under the Reference
> section.
> Nothing is missing from this page. The data simply does not live in
> the prose.

{/* GENERATED - do not edit. Source: the declaration named in the table below.
    Script: scripts/build-reference.mts. Change the doc comment on the symbol. */}

<PageTemplate kind="reference" />

## How this is generated [#how-this-is-generated]

Source: `lib/opsinjs.ts`. Script: `scripts/build-reference.mts`. Command:
`pnpm run generate`.

Everything below is copied from the symbol, so a page is improved by improving
its doc comment. The [API index](./index.mdx) says why there is a page per
symbol and what these pages still do not carry.

{/* opsinjs:generated:begin - everything below is replaced by scripts/build-reference.mts */}

## UnitConversion [#unitconversion]

An exact conversion between two units of the same kind.

Applied as `to = from * numerator / denominator + offsetNumerator / offsetDenominator`. Every field is an integer, and that is deliberate: these are definitions rather than measurements, and a definition stored as a rounded decimal is an approximation wearing a definition's provenance.

`basis` names the definition each factor comes from. A conversion with no basis does not belong in this system: opsinjs does not own a clinical number, and the ones it does carry are the ones that are true by definition rather than by measurement.

| Kind      | Declared in      |
| --------- | ---------------- |
| interface | `lib/opsinjs.ts` |

```ts
export interface UnitConversion {
  from: string
  to: string
  numerator: number
  denominator: number
  offsetNumerator: number
  offsetDenominator: number
  basis: string[]
}
```

{/* opsinjs:generated:end */}