Conversion Runs locally Ready to use Built-in examples No tracking

Length Converter

Convert between nine length units with internationally defined factors. All calculations run locally in your browser.

Measuring a room uses metres, buying a screen uses inches, a marathon is counted in kilometres, navigation uses nautical miles — length spans metric and imperial. This tool converts between millimetres, centimetres, metres, kilometres, inches, feet, yards, miles and nautical miles; the anchors are 1 inch = 2.54 cm exactly, 1 mile = 1.609344 km and 1 nautical mile = 1852 m.

Points of confusion: feet and inches are duodecimal, so 5 feet 7 inches is 5 × 12 + 7 = 67 inches, about 170 cm — never treat a height as decimal; the nautical mile belongs to sea and air navigation, defined as one minute of latitude, and is not used for land distances; and a screen size is the diagonal in inches, excluding the bezel.

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How to use

  1. Enter the length and pick its unit.
  2. Read the value in all the other units.
  3. Convert feet and inches through inches, not as decimals.
  4. Reserve nautical miles for navigation.

How it works

The conversion formula

Formula: result = value x source-unit factor / target-unit factor. All factors are based on the meter: 1 mm = 0.001 m, 1 inch = 0.0254 m, 1 mile = 1609.344 m.

Kilometers-to-miles example

Example: 100 km to miles. 100 x 1000 / 1609.344 = 62.1371, so 100 kilometers is about 62.14 miles.

Mental-math shortcuts

Mental math: meters to feet multiply by about 3.28, meters to yards by about 1.09, and kilometers to miles by about 0.62 (roughly kilometers x 0.6 gives miles).

Code example

JavaScript A coefficient table with metres as the hub 

const M = { mm: 0.001, cm: 0.01, m: 1, km: 1000,
            in: 0.0254, ft: 0.3048, yd: 0.9144,
            mi: 1609.344, nmi: 1852 };

const convert = (v, from, to) => v * M[from] / M[to];

convert(170, "cm", "in");     // 66.93 in
convert(26.2, "mi", "km");    // 42.16 (a marathon)

Python Converting a height in feet and inches 

IN = 0.0254

total_in = 5 * 12 + 7          # 5 feet 7 inches
cm = total_in * IN * 100       # 170.18 cm

# And back:
inches = 170 / (IN * 100)      # 66.93
ft, inch = divmod(inches, 12)  # 5 ft 6.93 in

FAQ

Why is 1 mile exactly 1609.344 meters?

The 1959 international yard-and-pound agreement defined 1 yard as exactly 0.9144 m, and 1 mile = 1760 yards, so 1 mile = 1760 x 0.9144 = 1609.344 m — the international standard definition.

How does a nautical mile differ from a mile?

A nautical mile is 1852 m, defined by one minute of arc on Earth, used in navigation and aviation; a (statute) mile is 1609.344 m, used on land. One nautical mile is about 1.15 miles.

How can I quickly estimate meters and feet?

1 m is about 3.28 ft. For a rough figure, multiply meters by 3 and add a third of the meters again. For example 1.8 m is about 1.8 x 3 + 0.6 = 6 ft (the precise value is 5.9055 ft).

Why are results exact rather than rounded?

Length units have precise international definitions (1 inch equals exactly 25.4 mm), so the factors carry no error; results are only rounded for display. For high precision, convert in one step to avoid compounding error across multiple conversions.

Which is longer, a yard or a meter?

1 yard = 0.9144 m, slightly shorter than a meter, so 100 yards is about 91.44 m. The 100 yards on an American football field is roughly 91.4 m. When you see "yard," confirm it means the imperial yard, not a loose Chinese phrasing.

Where is length conversion commonly needed?

Reading overseas product sizes (inches, feet on price tags), running distance and pace (miles/km), nautical distance (nautical miles), and renovation or drawings (mm/cm/m). For overseas shopping, convert to centimeters first before checking size charts.

Kilometer, mile and nautical mile are easy to confuse — how to remember?

Kilometer is metric (1 km = 1000 m); mile is imperial (1 mile is about 1.609 km); nautical mile is for sea and air (1 nmi = 1852 m, about 1.852 km). By length: nautical mile > mile > kilometer, and none are equal.