PhysicsCalcs
Units & Conversions

Length Converter

Convert meters, kilometers, centimeters, inches, feet, yards, miles, nautical miles, light-years, and parsecs.

Interactive converter

Length Converter

Convert meters, kilometers, centimeters, inches, feet, yards, miles, nautical miles, light-years, parsecs, and more.

Physical length is normally non-negative. Very large or small results may use scientific notation.

From
To

Result

Enter a value and click Convert to see the conversion.

Quick Guide

  • Enter a length value and select from/to units.
  • Use presets for common conversions like cm↔in or km↔mi.
  • Switch to All units to see every equivalent at once.

Table of Contents

Key Takeaways

  • The SI base unit of length is the meter (m).
  • 1 inch = 0.0254 m exactly; 1 foot = 0.3048 m exactly.
  • 1 mile = 1,609.344 m; 1 nautical mile = 1,852 m exactly.
  • 1 AU = 149,597,870,700 m exactly (IAU definition).
  • US survey foot differs slightly from the international foot — check labels for legacy survey units.

What Is a Length Converter?

It converts distance values between metric, imperial, US survey, nautical, astronomical, and scientific length units using meters as the internal reference.

For two-dimensional measurements, see the Area Converter. For wave-related distances, try the Frequency to Wavelength Calculator or Wavelength to Frequency Calculator.

Length Conversion Formula

valueB=valueA×(factorA/factorB)value_B = value_A × (factor_A / factor_B)

All units convert through meters as the base. Example: 1 in = 0.0254 m, so 12 in = 12 × 0.0254 = 0.3048 m = 1 ft.

Metric Prefix Ladder

SI length units scale by powers of 10: 1 km = 1,000 m, 1 m = 100 cm, 1 cm = 10 mm. Prefixes from femto (10⁻¹⁵) to exa (10¹⁸) cover everything from atomic to planetary scales.

Imperial & US Customary Units

Key exact definitions: 1 in = 0.0254 m, 1 ft = 0.3048 m, 1 yd = 0.9144 m, 1 mi = 1,609.344 m. These differ from legacy US survey units, which use the survey foot (1200/3937 m).

Nautical & Astronomical Units

1 nmi = 1,852 m. 1 AU = 149,597,870,700 m. 1 Julian light-year ≈ 9.461×10¹⁵ m. 1 parsec ≈ 3.086×10¹⁶ m. Astronomical units are approximate where noted.

Reference Scales

ScaleExampleMeters
Metric1 km1,000 m
Everyday1 ft0.3048 m
Navigation1 nmi1,852 m
Solar system1 AU1.496×10¹¹ m
Interstellar1 ly≈ 9.461×10¹⁵ m

Examples

1 km to m

1 km = 1,000 m.

1 inch to m

1 in = 0.0254 m exactly.

1 mile to km

1 mi = 1.609344 km.

1 nautical mile

1 nmi = 1.852 km exactly.

Common Mistakes

Confusing nautical miles with statute miles. Mixing US survey foot with international foot. Treating light-years as time units. Using screen pixels as physical length without noting CSS reference pixels differ from device pixels.

Limitations

Regional and historical units (cubit, vara, barleycorn) are omitted until verified factors are available. Astronomical constants use CODATA/IAU values marked approximate where applicable.

FAQ

How many meters in a kilometer?›

1 km = 1,000 m exactly.

How many centimeters in an inch?›

1 in = 2.54 cm exactly (since 1 in = 0.0254 m).

How many feet in a meter?›

1 m ≈ 3.28084 ft. To convert feet to meters, divide by 3.28084 or multiply by 0.3048.

How do I convert feet to meters?›

Multiply feet by 0.3048. Example: 10 ft = 3.048 m exactly.

How do I convert meters to feet?›

Divide meters by 0.3048, or multiply by 3.28084. Example: 1 m ≈ 3.28084 ft.

What is a nautical mile?›

1 international nautical mile = 1,852 m exactly, used in aviation and marine navigation.

What is a light-year?›

The distance light travels in one Julian year ≈ 9.461×10¹⁵ m. It is a unit of distance, not time.

What is an astronomical unit?›

1 AU = 149,597,870,700 m — the mean Earth–Sun distance.

US survey foot vs international foot?›

The US survey foot = 1200/3937 m ≈ 0.3048006096 m, slightly longer than the international foot (0.3048 m).

What is a parsec?›

1 pc ≈ 3.086×10¹⁶ m — the distance at which 1 AU subtends 1 arcsecond.

Sources

  1. BIPM: SI Brochure
  2. NIST SP 811: Guide for SI Units
Manish Kumar

Author & technical reviewer

Manish Kumar

PhysicsCalcs tools are reviewed with an educational focus: clear formulas, transparent assumptions, and practical context for students and science learners.

Learn more about Manish