Free · Length and area converters 📐

Length, Customary Units and Astronomical Scales

Convert lengths across metric, international customary, nautical and astronomical units, including the historical US survey foot.

  • Formula & worked example
  • Private in your browser
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

1 meter equals exactly 100 centimeters, 1000 millimeters and 0.001 kilometer.

1 inch = 0.0254 m; 1 nautical mile = 1852 m; 1 au = 149597870700 m; 1 pc = 648000 au/π.

Worked example

Enter these known values and leave the other values blank.

Length in meters
1 m
Length in millimeters
1000 mm
Length in centimeters
100 cm
Length in kilometers
0.001 km
Length in other metric units
1 m
Length in inches
39.37 in
Length in feet
3.281 ft
Length in yards
1.0936 yd
Length in miles
0.0006214 mi
Length in other imperial units
3.281 ft
Length in nautical miles
0.00054 nmi
Length in Sun radii
1.4374e-9 R☉
Length in light years
1.057e-16 ly
Length in other units
0.00054 nmi

Assumptions and limitations

  • The ordinary foot is the international foot, exactly 0.3048 m. The separate survey foot is exactly 1200/3937 m and is retained for historical data; it was retired for new US use in 2023.
  • A light-year uses the distance light travels in exactly 365.25 days. The solar radius is the IAU nominal 695700000 m scale; Earth radius here is a conventional mean 6371000 m. Neither asserts an actual instantaneous body radius.
  • Clear the value you want to solve before entering the remaining independent measurements. Display rounding does not describe measurement uncertainty.

Common questions

How should I enter an unknown quantity?

Leave the unknown field empty. Supply enough independent values; lock a known value if you need to preserve it while changing another control.

References

Replace rounded captured unit factors with exact definitions or explicitly identified CODATA 2022 central values; preserve all choices and original captures.

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