Length Converter
Convert a length or distance between metric units (nanometers to kilometers), imperial and US units (thou, inches, feet, yards, furlongs, miles) and nautical or astronomical units (fathoms, nautical miles, astronomical units, light-years). The result is calculated with exact factors, so 1 mile comes out as exactly 1.609344 km rather than a rounded approximation.
Convert a Length or Distance
Every factor is an exact legal definition (for example 1 inch = 25.4 mm). Negative lengths are accepted and converted mathematically.
Result
Same value in every length unit
How to Use the Length
- Type the value you want to convert in Value to convert.
- Pick the starting length unit in From unit and the one you want in To unit. The lists are grouped by measurement system.
- Read the result and the formula directly under the form; it updates as you type. Use Swap units to reverse the direction.
- Scroll to the table to see the same value in every available unit, change Precision if you need fewer digits, or press Copy result.
About This Tool
Travelers reading road signs abroad, runners and cyclists comparing routes, DIY builders and engineers mixing metric and imperial drawings, pilots and sailors, and students checking physics homework.
Input: A number and a unit · Output: The same length in every unit.
Features and Limitations
Features
- Exact definitions: 1 yd = 0.9144 m, 1 mi = 1609.344 m, 1 nautical mile = 1852 m, 1 au = 149 597 870 700 m.
- Sixteen units from nanometers to light-years, grouped into metric, imperial/US and nautical/astronomical.
- Shows a ready-to-use formula such as km = mi × 1.609344 and the one-unit equivalence line.
- Full table of the same length in every unit, with a Copy button for the headline result.
Limitations
- The foot used here is the international foot (0.3048 m). The older US survey foot (1200/3937 m) differs by about 2 parts per million and is not offered.
- A light-year is defined as the distance light travels in a Julian year; the result is exact, but a distance in light-years is rarely known that precisely.
- Results are computed in your browser; nothing you enter is sent to a server.
Example
5 mi = 8.04672 km. 6 ft = 1.8288 m. 100 m = 109.3613 yd (a 100-meter sprint is a little over 109 yards). A marathon of 42.195 km is 26.2188 mi, which is the familiar 26 miles 385 yards. 1 in = 25.4 mm exactly, so 5.5 in = 13.97 cm.
Frequently Asked Questions
Is an inch exactly 25.4 millimeters?
Yes. The international yard and pound agreement of 1959 defined the yard as exactly 0.9144 m, which makes 1 inch exactly 25.4 mm and 1 foot exactly 304.8 mm. The converter uses these exact numbers.
What is the difference between a mile and a nautical mile?
A statute mile is 1609.344 m. A nautical mile is 1852 m, originally one minute of latitude, so it is about 1.1508 statute miles. Distances at sea and in the air are quoted in nautical miles; road distances in the UK and US use statute miles.
Why do some US surveys use a slightly different foot?
Until the end of 2022 the US kept the survey foot (1200/3937 m) for land surveying. It is about 2 mm per kilometer longer than the international foot. Surveyors working from old coordinates should check which one their data uses; everyday conversions should use the international foot offered here.
Can I enter a negative length?
Yes. A negative number is simply converted with the same factor, which is handy for offsets, elevations below a datum or coordinates. The result keeps the minus sign.
How many digits are shown?
Automatic mode shows the exact result when it has 15 or fewer significant digits and otherwise rounds to 12 significant digits. Choose a number of decimal places or significant digits if you need a fixed format.
Related Tools
More like this: all Unit Converters tools, all Converters tools or the TinySandy home page.