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Light-Year, Kilometer & Astronomical Distance Converter

Convert light-years to metric distances, customary distances and astronomical units using a Julian-year light-year.

  • Formula & worked example
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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.

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

Formula and method

One light-year equals exactly 9,460,730,472,580,800 meters, or 9,460,730,472,580.8 kilometers. It is the distance light travels in vacuum at 299,792,458 m/s during 31,557,600 seconds.

Meters = light-years × 299792458 × 31557600; astronomical units = meters ÷ 149597870700

Worked example

Enter these known values and leave the other values blank.

Distance in light-years
1 ly
Metric distance
9460730472581 km
Customary distance
5878625373184 mi
Astronomical distance unit
63241 au

Assumptions and limitations

  • Uses a Julian year of exactly 365.25 days for the light-year and the exact astronomical unit of 149,597,870,700 m. Distances must be nonnegative.
  • This converts distance units. It does not infer a cosmological distance from redshift or model cosmic expansion, gravity or travel through a medium.
  • The optional Earth-radius scale uses 6,371,000 m and the solar-radius scale uses 695,700,000 m as reference values. They are scale conventions here, not live measurements of those bodies.

Common questions

Is a light-year a unit of time?

No. It is a distance defined using a year of light travel in vacuum. The word year describes the interval used in its definition.

Does this use 365 or 366 days?

Neither. The light-year uses the fixed Julian year of 365.25 days, independent of any particular calendar year.

References

The light-year uses exactly 299792458 m/s times a 31557600-second Julian year, replacing the rounded reference factor.

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