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Length Converter

Converts a length or distance between metric (nm to km), imperial/US (in, ft, yd, mi), nautical and astronomical units using exact NIST factors (1 in = 0.0254 m, 1 mi = 1609.344 m).

When to use

You need a distance, height or length in a different unit, e.g. miles to kilometres, feet to metres or inches to centimetres.

Do not use when: You need an area (use area), a volume (use volume), or a speed (use speed); for walking distance from step counts use steps-to-distance.

Formula

result = value × factor, factor = (1 from_unit in m) / (1 to_unit in m)

Inputs

Parameter	Type	Required	Description
`value`	number	yes	Amount to convert, expressed in from_unit.
`from_unit`	enum: nm \| um \| mm \| cm \| m \| km \| in \| ft \| yd \| mi \| nmi \| fathom \| au \| ly	yes	Unit of the input value. Accepted symbols: nm, um, mm, cm, m, km, in, ft, yd, mi, nmi, fathom, au, ly; spelled-out names and common abbreviations are accepted too.
`to_unit`	enum: nm \| um \| mm \| cm \| m \| km \| in \| ft \| yd \| mi \| nmi \| fathom \| au \| ly	yes	Unit to convert into (same symbols as from_unit).

Outputs

Output	Type	Description
`result`	number	Converted value expressed in to_unit (rounded to 6 decimals; see result_text for very small or very large values).
`result_text`	string	The conversion as text with 6 significant figures, e.g. "5 mi = 8.04672 km".
`formula`	string	Relation used, e.g. "1 mi = 1.609344 km".
`factor`	number	Multiplier from from_unit to to_unit (result = value × factor); absent for non-linear conversions.
`conversion_table`	object	The input value expressed in every supported length unit (6 significant figures), keyed by unit symbol.

Example

5 miles to kilometres: {"value":5,"from_unit":"mi","to_unit":"km"} → {"result":8.04672,"factor":1.609344,"formula":"1 mi = 1.609344 km","result_text":"5 mi = 8.04672 km","conversion_table":{"m":8046.72,"ft":26400}}

6 feet to centimetres: {"value":6,"from_unit":"ft","to_unit":"cm"} → {"result":182.88,"factor":30.48,"conversion_table":{"in":72,"m":1.8288}}

GET https://tttkmbb.com/api/v1/calculate/length?value=5&from_unit=mi&to_unit=km

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/length (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/length · Markdown: https://tttkmbb.com/conversion/length.md · JSON definition: https://tttkmbb.com/conversion/length.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="length"
OpenAPI operationId: convert_length
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

FAQ

Which mile is used?

The international statute mile (1609.344 m exactly). Nautical miles (1852 m) are the separate unit nmi.

Are the factors exact?

Yes for all SI and customary units: 1 in = 25.4 mm exactly by the 1959 international yard and pound agreement, so ft, yd and mi are exact multiples. The light-year uses the IAU Julian year (9 460 730 472 580 800 m).

Related calculators

Area Converter — Convert square units of the same lengths.
Speed Converter — Convert distance-per-time units such as mph and km/h.
Steps to Distance Calculator — Turn step counts into distance.