Astronomical Distance Converter

Enter one distance in any unit and instantly see its equivalent in meters, kilometers, AU, light-years, parsecs, kiloparsecs, megaparsecs, and gigaparsecs — plus the light-travel time.

Distance converter

Meters1.496 × 10¹¹ m
Kilometers1.496 × 10⁸ km
Astronomical unitsentered1 AU
Light-years1.5813 × 10⁻⁵ ly
Parsecs4.8481 × 10⁻⁶ pc
Kiloparsecs4.8481 × 10⁻⁹ kpc
Megaparsecs4.8481 × 10⁻¹² Mpc
Gigaparsecs4.8481 × 10⁻¹⁵ Gpc
Human heightEarth–MoonEarth–SunNearest starGalactic centerAndromedaObservable universeyour value — 1.496 × 10¹¹ m

Logarithmic scale — each step along the bar is a factor of ten, not an equal distance, so the marker's position reflects orders of magnitude, not a linear fraction of the way to the universe's edge.

Light-travel time8.3167 min

Astronomy runs on a different set of rulers depending on what’s being measured. A planetary orbit is naturally described in astronomical units; a nearby star, in light-years; the structure of the Galaxy, in kiloparsecs; the scale of the observable universe, in gigaparsecs. Converting between them by hand means chaining several huge or tiny multipliers together — this tool does it in one step: enter a distance in any unit and see it expressed in all of them at once.

The units, defined exactly

Every conversion here comes from three fixed physical definitions, not measured or approximate values:

1 AU=149,597,870,700 m(IAU 2012, exact)1\ \text{AU} = 149{,}597{,}870{,}700\ \text{m} \qquad \text{(IAU 2012, exact)} 1 pc=648000π AU(IAU 2015 — the distance at which 1 AU subtends 1 arcsecond)1\ \text{pc} = \frac{648000}{\pi}\ \text{AU} \qquad \text{(IAU 2015 — the distance at which 1 AU subtends 1 arcsecond)} 1 ly=c×365.25 days=9,460,730,472,580,800 m1\ \text{ly} = c \times 365.25\ \text{days} = 9{,}460{,}730{,}472{,}580{,}800\ \text{m}

using the SI-exact speed of light, c = 299,792,458 m/s, and the Julian year (365.25 days of 86,400 SI seconds) that “light-year” is conventionally defined against. Kiloparsecs, megaparsecs, and gigaparsecs are simply 10³, 10⁶, and 10⁹ parsecs. Because all of these are definitions rather than measurements, every conversion below is exact to floating-point precision — nothing here depends on an external API or a value that could later be refined.

Light-travel time

Distance and travel time are two sides of the same number once you fix a speed: light covers one light-year in exactly one year, by definition, so dividing any distance by c gives an intuitive second read on its scale — seconds for the Earth-Moon distance, minutes for the Earth-Sun distance, years for the nearest stars, and billions of years for the edge of the observable universe.