# Kilometers per hour to Miles per hour (km/h to mph)

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

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

## Formula

- `1 km/h = 0.621371 mph`
- `miles per hour = kilometers per hour × 0.6213711922`
- Reverse: `kilometers per hour = miles per hour × 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/h = 3.10686 mph
- 12.5 km/h = 7.76714 mph
- 100 km/h = 62.1371 mph

## Conversion table

| Kilometers per hour (km/h) | Miles per hour (mph) |
| --- | --- |
| 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%2Fh&to_unit=mph` → 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/h","to_unit":"mph"}`
- All speed units: https://tttkmbb.com/api/v1/units?quantity=speed · full converter: [Speed Converter](https://tttkmbb.com/conversion/speed.md)
- Authentication: none. Freshness: `static` (fixed conversion factors).

## FAQ

**How many miles per hour are in one kilometer per hour?**

1 km/h = 0.621371 mph. 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 per hour to miles per hour?**

Multiply the value in kilometers per hour by 0.6213711922: miles per hour = kilometers per hour × 0.6213711922. For example, 5 km/h = 3.10686 mph.

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

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

## Related conversions

- [Miles per hour to kilometers per hour](https://tttkmbb.com/conversion/mph-to-kmh.md) (reverse)
- [Meters per second to Kilometers per hour](https://tttkmbb.com/conversion/meters-per-second-to-kmh.md)
- [Kilometers per hour to Meters per second](https://tttkmbb.com/conversion/kmh-to-meters-per-second.md)
- [Meters per second to Miles per hour](https://tttkmbb.com/conversion/meters-per-second-to-mph.md)
- [Miles per hour to Meters per second](https://tttkmbb.com/conversion/mph-to-meters-per-second.md)
- [Knots to Kilometers per hour](https://tttkmbb.com/conversion/knots-to-kmh.md)
- [Kilometers per hour to Knots](https://tttkmbb.com/conversion/kmh-to-knots.md)
- [Knots to Miles per hour](https://tttkmbb.com/conversion/knots-to-mph.md)
- [Miles per hour to Knots](https://tttkmbb.com/conversion/mph-to-knots.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)