# Astronomical units to Kilometers (au to km)

> Convert astronomical units to kilometers: 1 au = 149598000 km. Exact conversion factor, formula, 22-row table and worked examples, with JSON API and MCP access.

- Page id: `au-to-km` · Quantity: Length (`length`, base unit m) · Tool: `convert_units`
- Canonical page: https://tttkmbb.com/conversion/au-to-km · This document: https://tttkmbb.com/conversion/au-to-km.md · JSON: https://tttkmbb.com/conversion/au-to-km.json (add `?value=` for a result)

## Formula

- `1 au = 149598000 km`
- `kilometers = astronomical units × 149597870.7`
- Reverse: `astronomical units = kilometers × 6.684587122e-9`

The factor follows from the SI definitions of both units (NIST SP 811); values below are rounded to 6 significant figures, the API returns up to 12.

## Worked examples

- 5 au = 747989000 km
- 12.5 au = 1869970000 km
- 100 au = 14959800000 km

## Conversion table

| Astronomical units (au) | Kilometers (km) |
| --- | --- |
| 1 | 149598000 |
| 2 | 299196000 |
| 3 | 448794000 |
| 4 | 598391000 |
| 5 | 747989000 |
| 6 | 897587000 |
| 7 | 1047190000 |
| 8 | 1196780000 |
| 9 | 1346380000 |
| 10 | 1495980000 |
| 15 | 2243970000 |
| 20 | 2991960000 |
| 25 | 3739950000 |
| 30 | 4487940000 |
| 40 | 5983910000 |
| 50 | 7479890000 |
| 75 | 11219800000 |
| 100 | 14959800000 |
| 200 | 29919600000 |
| 250 | 37399500000 |
| 500 | 74798900000 |
| 1000 | 149598000000 |

## API

- `GET https://tttkmbb.com/api/v1/convert?value=5&from_unit=au&to_unit=km` → unified JSON envelope with `result.values.result`, `formula`, `factor`, `sources`, `freshness`
- MCP: server `https://tttkmbb.com/mcp`, tool `convert_units` with `{"value":5,"from_unit":"au","to_unit":"km"}`
- All length units: https://tttkmbb.com/api/v1/units?quantity=length · full converter: [Length Converter](https://tttkmbb.com/conversion/length.md)
- Authentication: none. Freshness: `static` (fixed conversion factors).

## FAQ

**How many kilometers are in one astronomical unit?**

1 au = 149598000 km. 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 astronomical units to kilometers?**

Multiply the value in astronomical units by 149597870.7: kilometers = astronomical units × 149597870.7. For example, 5 au = 747989000 km.

**How do I convert kilometers back to astronomical units?**

Multiply by the inverse factor 6.684587122e-9 (astronomical units = kilometers × 6.684587122e-9), or use the kilometers-to-astronomical units page.

## Related conversions

- [Kilometers to astronomical units](https://tttkmbb.com/conversion/km-to-au.md) (reverse)
- [Kilometers to Miles](https://tttkmbb.com/conversion/km-to-miles.md)
- [Miles to Kilometers](https://tttkmbb.com/conversion/miles-to-km.md)
- [Meters to Feet](https://tttkmbb.com/conversion/meters-to-feet.md)
- [Feet to Meters](https://tttkmbb.com/conversion/feet-to-meters.md)
- [Centimeters to Inches](https://tttkmbb.com/conversion/cm-to-inches.md)
- [Inches to Centimeters](https://tttkmbb.com/conversion/inches-to-cm.md)
- [Millimeters to Inches](https://tttkmbb.com/conversion/mm-to-inches.md)
- [Inches to Millimeters](https://tttkmbb.com/conversion/inches-to-mm.md)

## Data Sources

- NIST Special Publication 811 – Guide for the Use of the International System of Units (SI), Appendix B conversion factors — https://www.nist.gov/pml/special-publication-811 (standard, retrieved 2026-09-24)
- BIPM – The International System of Units (SI Brochure, 9th edition) — https://www.bipm.org/en/publications/si-brochure (standard, retrieved 2026-09-24)
- Wikipedia – Conversion of units — https://en.wikipedia.org/wiki/Conversion_of_units (reference, retrieved 2026-09-24)