# Kilometers to Light-years (km to ly)

> Convert kilometers to light-years: 1 km = 1.057e-13 ly. Exact conversion factor, formula, 22-row table and worked examples, with JSON API and MCP access.

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

## Formula

- `1 km = 1.057e-13 ly`
- `light-years = kilometers × 1.057000834e-13`
- Reverse: `kilometers = light-years × 9460730473000`

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 km = 5.285e-13 ly
- 12.5 km = 1.32125e-12 ly
- 100 km = 1.057e-11 ly

## Conversion table

| Kilometers (km) | Light-years (ly) |
| --- | --- |
| 1 | 1.057e-13 |
| 2 | 2.114e-13 |
| 3 | 3.171e-13 |
| 4 | 4.228e-13 |
| 5 | 5.285e-13 |
| 6 | 6.34201e-13 |
| 7 | 7.39901e-13 |
| 8 | 8.45601e-13 |
| 9 | 9.51301e-13 |
| 10 | 1.057e-12 |
| 15 | 1.5855e-12 |
| 20 | 2.114e-12 |
| 25 | 2.6425e-12 |
| 30 | 3.171e-12 |
| 40 | 4.228e-12 |
| 50 | 5.285e-12 |
| 75 | 7.92751e-12 |
| 100 | 1.057e-11 |
| 200 | 2.114e-11 |
| 250 | 2.6425e-11 |
| 500 | 5.285e-11 |
| 1000 | 1.057e-10 |

## API

- `GET https://tttkmbb.com/api/v1/convert?value=5&from_unit=km&to_unit=ly` → 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":"km","to_unit":"ly"}`
- 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 light-years are in one kilometer?**

1 km = 1.057e-13 ly. 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 light-years?**

Multiply the value in kilometers by 1.057000834e-13: light-years = kilometers × 1.057000834e-13. For example, 5 km = 5.285e-13 ly.

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

Multiply by the inverse factor 9460730473000 (kilometers = light-years × 9460730473000), or use the light-years-to-kilometers page.

## Related conversions

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