Softonic

Length Converter

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Pick a source unit, enter a value, and see every other length unit update at once. The converter covers the SI metric ladder (mm, cm, m, km), the imperial staircase (in, ft, yd, mi), marine and aviation units (nautical mile), astronomy (light-year, AU) and typographic measures (point, pica) in one place, useful when a specification mixes half a dozen of them.

How to convert between length units

  1. 1

    Pick the source unit

    Cm, inches, feet, whatever the source document specifies.

  2. 2

    Type the value

    Decimals welcome: 2.54, 25.4, 1.85, 6.096.

  3. 3

    Read every other unit

    All targets update live; grab only the one you need.

  4. 4

    Copy the precision you want

    CAD needs 3 decimals, packaging 1, school homework 2. Choose before pasting.

All the conversion factors, with exact definitions

Since 1959 every imperial length has been defined by an exact fraction of a metre. No conversion here is an approximation; all are rational numbers that terminate in either decimal or fraction form.

Unit Exact metric equivalent
Inch (in) 25.4 mm (exactly)
Foot (ft) 0.3048 m (exactly)
Yard (yd) 0.9144 m (exactly)
Chain 20.1168 m (exactly)
Furlong 201.168 m (exactly)
Mile (statute) 1,609.344 m (exactly)
Nautical mile 1,852 m (exactly)
US survey foot 1200/3937 m (retired 2023)
Point (PostScript) 0.3527778 mm
Pica 4.2333333 mm
Ångström (Å) 1e-10 m
Astronomical unit 149,597,870,700 m
Light-year 9.4607 × 10¹⁵ m

When a unit is ambiguous

  • Mile: almost always statute (road). Say “nautical mile” when you mean navigation.
  • Gallon: (not a length, but the same trap) US liquid ≠ US dry ≠ imperial. Always specify.
  • Foot: international foot and US survey foot differ by 6 ppm. Trivial for furniture, matters for state-scale GIS.
  • Point: PostScript point (72 per inch) is the modern standard; traditional typographic point (72.27 per inch) still appears in LaTeX.

Precision and rounding advice

  • Machining: keep 4 decimals of mm; tolerances are often ±0.02 mm.
  • Architecture: round to 1 mm for residential, 10 mm for site surveys.
  • Packaging: 1 decimal of cm is usually enough; carriers round up for billing anyway.
  • Running: 1 decimal of km or 2 decimals of miles; GPS error dwarfs anything finer.
  • Atomic / microscopy: use nm or Å. A 1.54 Å C-C bond is 0.154 nm.

Common gotchas

  • 3 feet ≠ 1 yard in casual speech, but exactly is. 3 ft = 0.9144 m = 1 yd exactly.
  • Metric height is quoted as cm (180 cm), not m.m form (1.80 m) in most medical records.
  • Imperial height mixes feet and inches (5 ft 11 in), not decimals. Convert to decimal feet first if you need metric.

Frequently Asked Questions

The international yard and pound agreement of 1959 redefined the inch, foot and yard in terms of exact fractions of the metre. The US, UK, Canada, Australia and New Zealand all signed on; unit conversion became a matter of arithmetic rather than reference artifacts.

1 statute mile is 1,609.344 m (road and athletics); 1 nautical mile is 1,852 m (marine and aviation navigation). The nautical mile is one minute of arc along a meridian, which is why knots equal nautical miles per hour.

Only for land records and GIS work in the US predating 1 January 2023. NOAA retired it from federal mapping on that date; construction and everyday life have always used the international foot.

Yes, all conversion is local to your browser and the lengths you type are not sent anywhere.

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