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Kilometers to Astronomical units (km to au)

Convert kilometers to astronomical units: 1 km = 6.68459e-9 au. Exact conversion factor, formula, 22-row table and worked examples, with JSON API and MCP access.

Formula

1 km = 6.68459e-9 au

astronomical units = kilometers × 6.684587122e-9 — reverse: kilometers = astronomical units × 149597870.7

The factor is derived from the SI definitions of both units (base unit: m) as listed in NIST SP 811; results on this page are shown to 6 significant figures, the API returns up to 12.

Worked examples

Kilometers to astronomical units conversion table

Kilometers (km)Astronomical units (au)
16.68459e-9
21.33692e-8
32.00538e-8
42.67383e-8
53.34229e-8
64.01075e-8
74.67921e-8
85.34767e-8
96.01613e-8
106.68459e-8
151.00269e-7
201.33692e-7
251.67115e-7
302.00538e-7
402.67383e-7
503.34229e-7
755.01344e-7
1006.68459e-7
2000.00000133692
2500.00000167115
5000.00000334229
10000.00000668459

FAQ

How many astronomical units are in one kilometer?

1 km = 6.68459e-9 au. The factor comes from the SI definitions of both units (NIST SP 811 / BIPM), so it is exact or correct to at least 10 significant figures.

What is the formula to convert kilometers to astronomical units?

Multiply the value in kilometers by 6.684587122e-9: astronomical units = kilometers × 6.684587122e-9. For example, 5 km = 3.34229e-8 au.

How do I convert astronomical units back to kilometers?

Multiply by the inverse factor 149597870.7 (kilometers = astronomical units × 149597870.7), or use the astronomical units-to-kilometers page.

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