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Length Converter

A length converter for cm to inches and inches to cm, mm to inches, metres to feet and every other metric and imperial length, all shown alongside.

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Runs entirely in your browser. What you enter stays on your device — nothing is sent to a server. Verify it yourself

How many centimetres are in an inch?

Exactly 2.54. This is a definition rather than a measurement — the international agreement of 1959 defined the inch as exactly 0.0254 metres — so the conversion carries no error of its own.

Cost
Free, no limits
Upload
None — runs on your device
Sign-up
Not required
Works offline
Yes, once loaded

How to convert cm to inches

  1. Enter the value

    Type the number into the Value box; the result updates as you type.

  2. Choose the units

    Pick From and To — centimetres and inches to begin with, or anything from millimetres to nautical miles. The swap button between them flips the direction.

  3. Read every unit at once

    The All units table below the result shows the value in every length unit, metric and imperial.

Examples

  • 10 km6.2137 miles

    The conversion most people want for running distances.

  • 6 ft1.8288 m

    An inch is defined as exactly 25.4 mm, so this is exact.

Key features of the Length Converter

  • Converts between 9 length units
  • Converts as you type, in both directions
  • Metric and imperial in the same list
  • Runs entirely in your browser

Supported formats

Units

  • Millimetres
  • Centimetres
  • Metres
  • Kilometres
  • Inches
  • Feet
  • Yards
  • Miles
  • Nautical miles

When should you use this?

  • Converting a height or a room dimension between metric and imperial.
  • Reading a distance given in the other system.
  • Working with drawings or specifications in unfamiliar units.

Limitations

  • Conversions go through a base unit, so a value converted from one unit to another and back can differ in the last decimal place. That is floating-point arithmetic, not a defect, and it is far below the precision of any real measurement.
  • Results are displayed rounded for readability. If you need a specific number of significant figures, round the displayed value yourself rather than assuming the display is exact.
  • Converting a measurement cannot make it more precise than it was. A length measured to the nearest centimetre is still that precise after conversion, however many decimal places appear.
  • A nautical mile is 1,852 metres by definition and is not the same as a statute mile. Confusing the two in navigation is a substantial error.

Troubleshooting

The answer disagrees with another converter

Usually a different definition of the same unit name — US versus imperial, or a short versus a long ton. Check which variant each tool means before assuming one is wrong.

The last decimal place changes on a round trip

Conversion factors are not exact in binary floating point. The error is around one part in ten thousand billion, which no physical measurement can detect.

Common mistakes to avoid

  • Assuming a unit name is unambiguous. It very often is not.
  • Rounding partway through a multi-step calculation instead of at the end.

Pro tips

Tips for better results

  • US and UK units

    The same unit name can mean two amounts

    Check which system a unit belongs to before trusting it. Several unit names mean different amounts in the US and the UK.

  • Working method

    Write the unit beside every number

    Carry the unit through your working rather than converting at the end. Most unit errors happen when a number is written down without one.

  • Exactness

    The inch is exactly 25.4 mm, so these conversions are exact

    The inch has been defined as exactly 25.4 mm since 1959, so metric–imperial length conversions are exact rather than approximate.

Standards and terms behind the Length Converter

The named things this tool works with, and the documents that define them.

SI unitsSpecification
The international system of units, maintained by the BIPM, which fixes the metre, kilogram, second and kelvin. Reference: SI units
Imperial and US customary unitsSpecification
Inches, feet, pounds, gallons and Fahrenheit — still standard in the United States and common in the UK.

Also searched as: cm to inches, feet and inches to metres, miles to km, mm to inches chart.

Exact conversions, not approximations

The imperial units here are defined exactly in terms of the metre by the 1959 international agreement: an inch is exactly 0.0254 m, a foot exactly 0.3048 m, a mile exactly 1609.344 m. These are definitions, not measurements, so the conversions carry no error of their own.

One exception worth knowing: the US survey foot, used in American land surveying until 2023, was very slightly different — 1200/3937 m rather than 0.3048. The difference is about 2 parts per million, invisible for everyday work and significant across a state.

Reading the results

Results use significant digits rather than a fixed number of decimals. Rounding to two decimals would render 1 mm in miles as "0.00", and eight decimals would render 1 km in metres as "1000.00000000". Neither is a useful answer, so the precision adapts to the magnitude.

Privacy

The Length Converter runs entirely in your browser. What you enter and the result it produces stay on your own device — nothing is sent anywhere, because nothing needs to be.

You can confirm this rather than take our word for it: open your browser’s developer tools, watch the Network tab, and use the tool. No request carries your input. It also keeps working with the connection off.

Details are in the privacy policy.

More unit converters

What next?

Area does not scale the way length does — doubling a length quadruples the area.

Convert areas

Length Converter — questions

How do I convert feet to meters?

Multiply by 0.3048 — a foot is exactly 0.3048 m — so 6 ft is 1.8288 m. For meters to feet, divide by 0.3048: 1 m is about 3.28084 ft.

How many centimetres are in an inch?

Exactly 2.54 cm. This is a definition rather than a measurement, so the conversion is exact.

How do I convert feet to metres?

Multiply by 0.3048, which is exact by definition. 6 feet is 1.8288 m.

What is a nautical mile?

Exactly 1852 metres — roughly one minute of latitude. It is used in marine and air navigation because it maps directly onto degrees on a chart.

Why do the results show a varying number of decimals?

The tool uses significant digits, so precision follows the magnitude. A fixed decimal count would show tiny values as zero and large ones with meaningless trailing digits.

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