Free · Length conversions

Astronomical Units, Light-Years & Parsecs

Convert astronomical units to meters, kilometers, light-years, parsecs and their million-unit scales.

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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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Formula and method

One astronomical unit is exactly 149,597,870,700 m or 149,597,870.7 km. It is a defined distance unit, not today’s Earth–Sun separation.

Meters = astronomical units × 149,597,870,700; parsecs = astronomical units × π ÷ 648,000

Worked example

Enter these known values and leave the other values blank.

Astronomical units
1 au
Meters
149597870700 m
Kilometers
149597871 km
More metric units
14959787070000 cm
Light years
0.000015813 ly
Parsecs
0.000004848 pcs
Solar radii
215.03 R☉ (nominal)
More astronomical units
1.5813e-11 Mly
Miles
92955807 mi
More imperial/US units
163602220801 yd

Assumptions and limitations

  • International units use exactly 25.4 mm per inch, 0.3048 m per foot, 0.9144 m per yard and 1,609.344 m per statute mile. A nautical mile is exactly 1,852 m.
  • Every field describes the same length. Zero and signed values are supported for directed measurements; a negative result does not describe a physical size. Display rounding does not increase the precision of the original measurement.
  • In a compound feet/inches field, use a colon: 1:6 means one foot six inches. Decimal 1.6 feet is one foot 7.2 inches. Read the selected unit when editing a flexible field.
  • A light-year is the distance light travels in vacuum in one 365.25-day Julian year: 9,460,730,472,580,800 m. A parsec is 648,000/π astronomical units; an astronomical unit is exactly 149,597,870,700 m. Mly and Mpc mean one million of their respective units.
  • The nominal solar-radius comparison uses 695,700,000 m. The optional Earth-radius comparison retains a fixed 6,371,000 m mean-radius scale. Neither option measures the actual radius at a chosen location or time.

Common questions

Is a light-year a unit of time?

A light-year measures distance. The year specifies how long light travels in vacuum to define that distance; the converter itself does not calculate an object’s travel time.

Does one AU always equal the current Earth–Sun distance?

No. The astronomical unit has a fixed definition, while the separation of Earth and the Sun varies along the orbit.

Can I work backward from a result?

Yes. Enter the known length in any editable field to update the other representations. Check the selected unit first, especially in the flexible comparison fields.

Why does changing a unit change the number?

The length stays the same while the size of the unit changes. A longer unit needs a smaller number of units to represent the same distance.

References

The light-year uses exactly 299792458 m/s times a 31557600-second Julian year, replacing the rounded reference factor. The parsec uses the IAU definition 648000/π astronomical units, with one astronomical unit exactly 149597870700 meters, instead of a rounded decimal factor. A million light-years uses exactly one million Julian light-years, consistently with the reviewed single light-year unit. A megaparsec uses exactly one million IAU-defined parsecs, consistently with the reviewed single parsec unit.

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