# Kilometers to Miles (km to mi)

> Convert kilometers to miles: 1 km = 0.621371 mi. Exact conversion factor, formula, 22-row table and worked examples, with JSON API and MCP access.

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

## Formula

- `1 km = 0.621371 mi`
- `miles = kilometers × 0.6213711922`
- Reverse: `kilometers = miles × 1.609344`

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 = 3.10686 mi
- 12.5 km = 7.76714 mi
- 100 km = 62.1371 mi

## Conversion table

| Kilometers (km) | Miles (mi) |
| --- | --- |
| 1 | 0.621371 |
| 2 | 1.24274 |
| 3 | 1.86411 |
| 4 | 2.48548 |
| 5 | 3.10686 |
| 6 | 3.72823 |
| 7 | 4.3496 |
| 8 | 4.97097 |
| 9 | 5.59234 |
| 10 | 6.21371 |
| 15 | 9.32057 |
| 20 | 12.4274 |
| 25 | 15.5343 |
| 30 | 18.6411 |
| 40 | 24.8548 |
| 50 | 31.0686 |
| 75 | 46.6028 |
| 100 | 62.1371 |
| 200 | 124.274 |
| 250 | 155.343 |
| 500 | 310.686 |
| 1000 | 621.371 |

## API

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

1 km = 0.621371 mi. 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 miles?**

Multiply the value in kilometers by 0.6213711922: miles = kilometers × 0.6213711922. For example, 5 km = 3.10686 mi.

**How do I convert miles back to kilometers?**

Multiply by the inverse factor 1.609344 (kilometers = miles × 1.609344), or use the miles-to-kilometers page.

## Related conversions

- [Miles to kilometers](https://tttkmbb.com/conversion/miles-to-km.md) (reverse)
- [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)
- [Meters to Yards](https://tttkmbb.com/conversion/meters-to-yards.md)
- [Yards to Meters](https://tttkmbb.com/conversion/yards-to-meters.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)