# Length convert

`length-convert` · version 1.0.0 · Units & sizes · free, no key needed

Convert a canonical integer length between exact SI and international customary units.

**Use when you need to: length convert · convert length units · convert integer length between units.**

## Supported

- length convert
- convert length units
- convert integer length between units

## Not supported

- nautical miles
- survey feet
- SI prefixes other than nm um mm cm m km
- floating-point lengths

## Behavior

- value is a canonical integer string amount in the from unit and may be negative.
- from and to are exactly one of nm, um, mm, cm, m, km, in, ft, yd, mi using the LENGTH_NM table.
- The result is the reduced rational (value * from_nm) / to_nm expressed in to units.
- Sign lives only on the numerator; zero is numerator 0 over denominator 1.
- Input integers and the reduced numerator and denominator may have at most 1000 digits excluding sign.

## Input

- `value` (string, required): max length 1001; pattern `^-?(0|[1-9][0-9]*)$`
- `from` (one of "nm", "um", "mm", "cm", "m", "km", "in", "ft", "yd", "mi", required)
- `to` (one of "nm", "um", "mm", "cm", "m", "km", "in", "ft", "yd", "mi", required)

## Output

- `numerator` (string, required): pattern `^(0|-?[1-9][0-9]*)$`
- `denominator` (string, required): pattern `^[1-9][0-9]*$`

## Limits

- max digits: 1000
- units: ["nm","um","mm","cm","m","km","in","ft","yd","mi"]

## Example

Request input:

```json
{
  "value": "1",
  "from": "ft",
  "to": "in"
}
```

Response:

```json
{
  "result": {
    "numerator": "12",
    "denominator": "1"
  }
}
```

## How to call it

### MCP

Connect `https://computefirst.net/mcp` ([setup](/docs#connect)), then call `execute` with:

```json
{
  "id": "length-convert",
  "version": "1.0.0",
  "input": {
    "value": "1",
    "from": "ft",
    "to": "in"
  }
}
```

### HTTP (no key)

```sh
curl -X POST https://computefirst.net/v1/tools/length-convert/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"value":"1","from":"ft","to":"in"}'
```

The machine-readable contract is at [/v1/tools/length-convert/versions/1.0.0](/v1/tools/length-convert/versions/1.0.0).

### CLI

```sh
node cli.mjs run length-convert 1.0.0 --input input.json --base-url https://computefirst.net
```

Get the client at [/clients/cli/](/clients/cli/).

## Related tools

- [Byte size convert](/tools/bytesize-convert): Convert a non-negative integer byte size between IEC binary units as an exact rational.
- [Length compare](/tools/length-compare): Compare two integer length measurements by exact nanometer amounts.
- [Mass convert](/tools/mass-convert): Convert a canonical integer mass amount between exact nanogram-based units as a reduced rational.
- [Temperature convert](/tools/temperature-convert): Convert a decimal temperature between Celsius, Fahrenheit, and Kelvin as an exact rational.
- [Length add](/tools/length-add): Add integer length terms in mixed units and return the exact sum in a chosen unit.
- [Mass add](/tools/mass-add): Add mixed-unit canonical integer mass amounts and express the sum in a target unit as a reduced rational.