Use this Length Converter to convert measurements between metric, imperial/US, nautical, survey, and astronomy units. Enter a value in any supported field, click Calculate, and the converter updates the equivalent lengths in millimeters, centimeters, meters, kilometers, inches, feet, yards, miles, nautical miles, light years, astronomical units, parsecs, and more.

Important Note: This Length Converter uses standard meter-based conversion factors. It converts the entered value into meters first, then converts that meter value into the selected target units.

Use this tool for everyday, educational, construction, scientific, nautical, survey-reference, and astronomy-scale length conversions. For legal surveying, engineering drawings, aerospace navigation, metrology, regulated documentation, or safety-critical work, confirm the required unit definition, rounding rule, datum, and precision standard before relying on the result.

Reviewed by: AjaxCalculators Editorial Team
Last updated: April 29, 2026
Method source: Standard unit conversion through a meter base value using value_B = value_A × factor(A→m) ÷ factor(B→m)
Editorial standards: AjaxCalculators Editorial Policy

What This Length Converter Does

This calculator converts length values between common and specialized units. It works by converting the entered value into meters first, then converting that meter value into every other selected unit.

The converter can handle:

• Metric units, including mm, cm, m, km, μm, nm, pm, and Å
• Imperial and US units, including inches, feet, yards, miles, thou/mil, and kilofeet
• Mixed units, including meters/centimeters and feet/inches
• Fractional inch style input, including eighths of an inch
• Nautical miles
• Astronomy units, including astronomical units, light years, parsecs, megaparsecs, Earth radii, and Sun radii
• US survey feet for legacy survey-related conversions

How the Length Converter Works

The converter uses meters as the base unit. Every unit has a conversion factor to meters. Once the entered value is converted to meters, the calculator divides by the target unit’s meter factor to display the equivalent value.

Target value = input value × input-unit meter factor ÷ target-unit meter factor

Using symbols:

value_B = value_A × factor(A→m) ÷ factor(B→m)

For example, to convert feet to meters, the calculator uses:

1 ft = 0.3048 m

To convert meters back to feet, it divides by 0.3048.

Metric Length Units

Metric length units are based on powers of ten. The meter is the SI base unit for length, and smaller or larger metric units are formed using metric prefixes.

Metric Unit	Symbol	Equivalent in Meters
Picometer	pm	0.000000000001 m
Nanometer	nm	0.000000001 m
Micrometer	μm	0.000001 m
Millimeter	mm	0.001 m
Centimeter	cm	0.01 m
Decimeter	dm	0.1 m
Meter	m	1 m
Kilometer	km	1000 m
Ångström	Å	0.0000000001 m

Imperial and US Length Units

Imperial and US customary length units are commonly used in construction, real estate, woodworking, machining, road distances, and everyday measurements in the United States and some other contexts.

Unit	Symbol	Equivalent in Meters
Thou / mil	mil	0.0000254 m
Inch	in	0.0254 m
Foot	ft	0.3048 m
Yard	yd	0.9144 m
Mile	mi	1609.344 m
Kilofoot	kft	304.8 m
US survey foot	sft	1200/3937 m, approximately 0.3048006096 m

Other Supported Length Units

The converter also includes nautical, astronomy, and large-scale scientific distance units.

Unit	Symbol	Approximate Equivalent in Meters
Nautical mile	nmi	1852 m
Earth radius	R⊕	about 6,371,000 m
Sun radius	R☉	about 695,700,000 m
Astronomical unit	au	149,597,870,700 m
Light year	ly	about 9.460730472 × 1015 m
Parsec	pc	about 3.085677581 × 1016 m
Megalight year	Mly	1,000,000 ly
Megaparsec	Mpc	1,000,000 pc

Common Length Conversion Formulas

Conversion	Formula
Millimeters to meters	m = mm ÷ 1000
Centimeters to meters	m = cm ÷ 100
Kilometers to meters	m = km × 1000
Inches to meters	m = in × 0.0254
Feet to meters	m = ft × 0.3048
Yards to meters	m = yd × 0.9144
Miles to kilometers	km = mi × 1.609344
Nautical miles to meters	m = nmi × 1852

Worked Example: Convert Feet to Meters

Suppose you want to convert 6 feet to meters.

Step 1: Use the foot-to-meter factor
1 ft = 0.3048 m

Step 2: Multiply by the number of feet
meters = 6 × 0.3048

Step 3: Calculate
meters = 1.8288 m

So, 6 feet = 1.8288 meters.

Worked Example: Convert Meters to Feet and Inches

Suppose you want to convert 1.75 meters into feet and inches.

Step 1: Convert meters to feet
feet = meters ÷ 0.3048
feet = 1.75 ÷ 0.3048
feet ≈ 5.7415 ft

Step 2: Separate whole feet
Whole feet = 5 ft

Step 3: Convert the decimal feet to inches
0.7415 ft × 12 ≈ 8.90 in

So, 1.75 meters ≈ 5 ft 8.9 in.

Worked Example: Convert Miles to Kilometers

Suppose you want to convert 3 miles to kilometers.

Step 1: Use the mile-to-kilometer factor
1 mi = 1.609344 km

Step 2: Multiply
km = 3 × 1.609344

Step 3: Calculate
km = 4.828032 km

So, 3 miles ≈ 4.83 kilometers.

Worked Example: Convert Inches to Centimeters

Suppose you want to convert 12 inches to centimeters.

Step 1: Use the inch-to-centimeter factor
1 in = 2.54 cm

Step 2: Multiply
cm = 12 × 2.54

Step 3: Calculate
cm = 30.48 cm

So, 12 inches = 30.48 centimeters.

Worked Example: Convert Nautical Miles to Kilometers

Suppose you want to convert 5 nautical miles to kilometers.

Step 1: Use the nautical-mile conversion
1 nmi = 1852 m = 1.852 km

Step 2: Multiply
km = 5 × 1.852

Step 3: Calculate
km = 9.26 km

So, 5 nautical miles = 9.26 kilometers.

Worked Example: Convert Light Years to Meters

Suppose you want to convert 2 light years to meters.

Step 1: Use the light-year factor
1 ly ≈ 9.460730472 × 10¹⁵ m

Step 2: Multiply
meters = 2 × 9.460730472 × 10¹⁵

Step 3: Calculate
meters ≈ 1.8921460944 × 10¹⁶ m

So, 2 light years is about 1.892 × 10¹⁶ meters.

How to Use This Length Converter

1. Enter a value in any supported length field.
2. Click Calculate.
3. Review the converted values in metric, imperial/US, nautical, and other units.
4. Use the dropdowns for “other metric units,” “other imperial units,” or “other units” when you need a less common unit.
5. Use mixed-unit fields such as m / cm or ft / in when your measurement is written in two parts.
6. Use the Copy meters button if you want the converted base-meter value.
7. Click Reset to clear the converter and start again.

How to Interpret the Results

Result Group	What It Shows	Best Used For
Metric results	Millimeters, centimeters, meters, kilometers, and other metric equivalents.	Science, engineering, education, international measurement, and general metric use.
Imperial / US results	Inches, feet, yards, miles, mils, and related US customary units.	US construction, woodworking, machining, road distances, real estate, and everyday measurement.
Mixed-unit results	Values such as meters/centimeters or feet/inches.	Human height, room measurements, construction measurements, and practical layout work.
Nautical miles	Distance in nautical miles.	Marine navigation, aviation, and geographic distance contexts.
Astronomy units	Astronomical units, light years, parsecs, and larger space-scale units.	Solar-system, stellar, and cosmological distance comparisons.
US survey feet	Legacy survey-foot equivalent.	Older survey, mapping, and coordinate datasets where the US survey foot is specifically required.

Metric vs Imperial Length Units

System	Common Units	Best Used For
Metric / SI	mm, cm, m, km	Science, engineering, international measurement, education, and most global use.
Imperial / US customary	in, ft, yd, mi	US construction, real estate, road distances, woodworking, and everyday US measurements.
Nautical	nmi	Marine navigation and aviation.
Astronomical	au, ly, pc, Mpc	Solar-system, stellar, and cosmological distances.

Mixed Units: Feet and Inches

Many everyday measurements are written in mixed feet and inches. The converter supports this style by converting the total measurement into inches first, then into meters.

Total inches = feet × 12 + inches

For example:

5 ft 8 in = (5 × 12) + 8 = 68 in

Then:

68 in × 0.0254 = 1.7272 m

So, 5 ft 8 in = 1.7272 m.

Mixed Units: Meters and Centimeters

Metric mixed units are also common, especially for height and short measurements.

Total meters = meters + centimeters ÷ 100

For example:

1 m 75 cm = 1 + 75 ÷ 100 = 1.75 m

Eighths of an Inch

The converter includes eighths of an inch for practical measurements used in construction, woodworking, sewing, and small layout work.

Total inches = whole inches + eighths ÷ 8

For example:

3 and 5/8 in = 3 + 5 ÷ 8 = 3.625 in

Then:

3.625 in × 2.54 = 9.2075 cm

When to Use Nautical Miles

A nautical mile is mainly used for navigation. It is common in marine, aviation, and geographic distance contexts.

Unit	Meters	Kilometers
1 statute mile	1609.344 m	1.609344 km
1 nautical mile	1852 m	1.852 km

Do not use statute miles and nautical miles interchangeably. A nautical mile is longer than a statute mile.

Astronomy Length Units

The converter includes astronomy units for very large distances.

Unit	Typical Use	Scale
Astronomical unit	Distances within the solar system	Approximately the average Earth-Sun distance
Light year	Distances to stars and galaxies	Distance light travels in one Julian year
Parsec	Professional astronomy and stellar distance	About 3.26 light years
Megaparsec	Large galaxy and cosmology distances	1,000,000 parsecs

These units are helpful for comparing large space distances, but they should not be mixed with everyday measurements unless scientific notation is appropriate.

US Survey Foot Note

The US survey foot is slightly different from the standard international foot. It is mainly relevant for older surveying, mapping, and coordinate datasets.

Foot Type	Definition	Use Note
International foot	0.3048 m exactly	Use for current general measurement.
US survey foot	1200/3937 m	Use only when required for legacy survey or mapping data.

NIST states that beginning January 1, 2023, the US survey foot should be avoided except for historic and legacy applications. For current general conversions, use the standard international foot.

Common Length Conversion Table

Input	Equivalent
1 in	2.54 cm
1 ft	0.3048 m
1 yd	0.9144 m
1 mi	1.609344 km
1 nmi	1.852 km
1 m	100 cm = 1000 mm
1 km	1000 m
1 au	149,597,870,700 m
1 ly	about 9.460730472 × 1015 m

Practical Uses

This Length Converter can be useful for:

• converting height between centimeters and feet/inches
• converting construction measurements
• checking woodworking or machining dimensions
• converting road distances between miles and kilometers
• converting map and survey measurements
• converting nautical miles for marine or aviation use
• checking scientific measurements in metric prefixes
• converting astronomy distances such as au, light years, and parsecs
• copying a meter-based value for other calculations

Common Mistakes to Avoid

• Do not confuse miles with nautical miles.
• Do not confuse feet with US survey feet in legacy survey data.
• Do not enter centimeters as meters unless you intentionally convert first.
• Do not use outside-rounded values when precision matters.
• Do not confuse mil as 0.001 inch with millimeter.
• Do not assume light years are a time unit; a light year is a distance.
• Do not use astronomical units for Earth-scale construction or map measurements.
• Do not round intermediate values too early when converting across many units.

Important Assumptions and Limitations

• This converter performs one-dimensional length and distance conversions only.
• It does not convert area, volume, speed, weight, mass, force, torque, pressure, or density.
• Most conversions are based on fixed meter conversion factors.
• Metric prefix conversions are based on powers of ten.
• Mixed-unit fields such as feet/inches and meters/centimeters are converted into a single base value before conversion.
• Fractional inch input using eighths is converted into decimal inches before conversion.
• Astronomy units such as Earth radius and Sun radius are practical reference values, not exact measurements for every real object or context.
• US survey feet are included for legacy data and should not be used for current general foot-based measurements unless a legacy dataset specifically requires them.
• Displayed values may be rounded for readability.
• For legal surveying, engineering drawings, aerospace navigation, metrology, regulated documentation, or safety-critical work, confirm the required unit definition, datum, rounding rule, and precision standard.

When You May Need a Different Calculator

This calculator is best for one-dimensional length conversion. You may need another calculator if you want to calculate:

• area from length and width
• volume from length, width, and height
• speed from distance and time
• map scale
• roof pitch or ramp slope
• pipe volume from diameter and length
• pixels to inches from PPI/DPI
• fractional inches for woodworking or machining

References

1. BIPM — SI Base Units: Metre
2. NIST Guide to the SI — Appendix B: Conversion Factors
3. NIST Guide to the SI — Appendix B.9: Length Conversion Factors
4. NIST — Approximate Conversions from U.S. Customary Measures to Metric
5. NIST — U.S. Survey Foot
6. NASA/JPL CNEOS — Astronomical Unit
7. International Astronomical Union — Measuring the Universe

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Length Converter Disclaimer

This Length Converter provides unit conversion estimates using standard meter-based conversion factors. It is suitable for everyday, educational, scientific, construction, navigation-reference, astronomy-reference, and general measurement use.

Results depend on the selected unit, entered value, conversion factor, and displayed rounding. For legal surveying, engineering drawings, aerospace navigation, metrology, regulated documentation, official mapping, or safety-critical work, confirm the required unit definition, datum, rounding rule, and precision standard before relying on the result.