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Length converter

Convert millimetres, feet, miles, and nautical miles without a spreadsheet.

This tool processes files and text locally in your browser. Your content is not uploaded or stored by this site.

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What this tool does

You enter an amount and two length units. ConvertPass multiplies by exact SI factors: the metre is the base, the inch is 0.0254 m, and a nautical mile is 1852 m. The result JSON also lists every other length in the menu from the same amount.

How to use it

  1. Enter the length.
  2. Pick the source and destination units.
  3. Convert, then copy the JSON or read the other units in the same family.

Supported input

  • A number and two length units from the menu

Output

  • JSON with the converted length plus every other unit in the family

Privacy

This tool processes files and text locally in your browser. Your content is not uploaded or stored by this site.

ConvertPass does not include your input in analytics, URLs, or error reports. Encoding: Decimal numbers / SI metre. Limit: A single length (4.0 KB).

Limitations

  • The US survey foot is not offered. These are international feet and miles.
  • Astronomical units, parsecs, and printer points are not in the menu.
  • Negative lengths are refused. This is a geometry calculator, not a signed-offset CAD kernel.

Example

Input
1 inch → millimetres
Output
{
  "result": 25.4,
  "formatted": "1 in = 25.4 mm"
}

The international inch is exact.

Troubleshooting

My construction drawing used US survey feet
This converter uses the international foot. Survey feet differ by two parts per million. Use a survey calculator for legal boundaries.

FAQ

Is a nautical mile the same as a statute mile?

No. A nautical mile is 1852 m. A statute mile is 1609.344 m.

What is a mil?

A thou: one thousandth of an international inch. It is not a millilitre and not a millimetre.

Can I convert light-years?

No. ConvertPass stays on laboratory and map lengths. Use an astronomy library for parsecs.

Does the page send the number anywhere?

No. The factors live in this JavaScript bundle. Conversion never leaves the tab.

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Related formats

Last reviewed 16 August 2026. Report a problem. Reports do not include your input.