# Light-years to Kilometers (ly to km)

> Convert light-years to kilometers: 1 ly = 9460730000000 km. Exact conversion factor, formula, 22-row table and worked examples, with JSON API and MCP access.

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

## Formula

- `1 ly = 9460730000000 km`
- `kilometers = light-years × 9460730473000`
- Reverse: `light-years = kilometers × 1.057000834e-13`

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 ly = 47303700000000 km
- 12.5 ly = 118259000000000 km
- 100 ly = 946073000000000 km

## Conversion table

| Light-years (ly) | Kilometers (km) |
| --- | --- |
| 1 | 9460730000000 |
| 2 | 18921500000000 |
| 3 | 28382200000000 |
| 4 | 37842900000000 |
| 5 | 47303700000000 |
| 6 | 56764400000000 |
| 7 | 66225100000000 |
| 8 | 75685800000000 |
| 9 | 85146600000000 |
| 10 | 94607300000000 |
| 15 | 141911000000000 |
| 20 | 189215000000000 |
| 25 | 236518000000000 |
| 30 | 283822000000000 |
| 40 | 378429000000000 |
| 50 | 473037000000000 |
| 75 | 709555000000000 |
| 100 | 946073000000000 |
| 200 | 1.89215e+15 |
| 250 | 2.36518e+15 |
| 500 | 4.73037e+15 |
| 1000 | 9.46073e+15 |

## API

- `GET https://tttkmbb.com/api/v1/convert?value=5&from_unit=ly&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":"ly","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 light-year?**

1 ly = 9460730000000 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 light-years to kilometers?**

Multiply the value in light-years by 9460730473000: kilometers = light-years × 9460730473000. For example, 5 ly = 47303700000000 km.

**How do I convert kilometers back to light-years?**

Multiply by the inverse factor 1.057000834e-13 (light-years = kilometers × 1.057000834e-13), or use the kilometers-to-light-years page.

## Related conversions

- [Kilometers to light-years](https://tttkmbb.com/conversion/km-to-light-years.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)