UrbiTools

AU to km Converter

Convert astronomical units to kilometres and back — the Earth–Sun distance, the solar system's own yardstick, in plain kilometres.

Convert AU ⇄ km

149597870.7 km
1 AU = 149597870.7 km

Formula: 1 AU (AU × 149,597,870.7) = 149597870.7 km

How the au to km conversion works

One astronomical unit is 149,597,870.7 kilometres — defined exactly by the International Astronomical Union in 2012 as 149,597,870,700 metres. So km = AU × 149,597,870.7, and AU = km ÷ 149,597,870.7. Before 2012 the AU wobbled slightly with better measurements of the solar system; since the redefinition it is a fixed, exact number, which makes this conversion exact rather than approximate.

The solar system in AU: Mercury orbits at 0.39 AU, Venus at 0.72 AU, Mars at 1.52 AU, Jupiter at 5.20 AU and Neptune at 30.07 AU — which is 30.07 × 149,597,870.7 = 4,498,407,972 km. Neptune's distance is a number nobody visualises; “30 AU” is instantly meaningful to anyone who knows the scale. That is the whole point of the unit: it keeps solar-system distances in human-sized numbers.

Beyond the planets: the Kuiper belt stretches roughly from 30 to 50 AU, and Voyager 1 — the most distant human-made object — passed 160 AU in the 2020s, still inside a solar system whose gravitational reach extends far beyond. One parsec, the professional astronomers' unit, is 206,265 AU. For distances to other stars, where even AU becomes unwieldy, switch to our light-years to km converter.

Handy benchmarks: 0.39 AU (Mercury) = 58,343,170 km, 1 AU (Earth) = 149,597,871 km, 5.20 AU (Jupiter) = 777,908,928 km, 30.07 AU (Neptune) = 4,498,407,972 km and 100 AU = 14,959,787,070 km. Light takes about 8 minutes 20 seconds to cross one AU — the “8 light-minutes” between us and the Sun.

au to km converter questions

How many km are in 1 AU?
One astronomical unit is exactly 149,597,870.7 km — the average Earth–Sun distance, fixed by the IAU in 2012 as 149,597,870,700 metres.
How do I convert AU to km?
Multiply astronomical units by 149,597,870.7: km = AU × 149,597,870.7. For example, Mars at 1.52 AU is 1.52 × 149,597,870.7 = 227,388,764 km from the Sun on average.
How far is Neptune from the Sun in km?
Neptune orbits at about 30.07 AU, which is 30.07 × 149,597,870.7 = 4,498,407,972 km — roughly 4.5 billion kilometres, or about 4 light-hours away.
Is an AU the same as a light-year?
No — very different scales. One light-year is about 63,241 AU, because light covers one AU in just 8 minutes 20 seconds. AU is for solar-system distances; light-years are for interstellar ones.
Why was the AU redefined in 2012?
Before 2012 the AU was defined from the Sun's apparent motion and shifted slightly as measurements improved. The IAU fixed it at exactly 149,597,870,700 metres so that ephemeris calculations and conversions like this one are exact and stable.

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Sources & official guidance

Exact conversion — 1 AU = 149,597,870.7 km (IAU 2012 definition). Planetary distances quoted are average orbital distances; actual distances vary along each orbit. See our disclaimer.