# How do I convert mph to km/h?

Converts miles per hour (mph) to kilometers per hour (km/h) and back, with the exact unit definitions.

- Page: https://www.acalculator.org/convert/mph-to-kmh
- JSON spec: https://www.acalculator.org/convert/mph-to-kmh.json
- Version: ce1aa9790423

## Default answer

Example with the default inputs (Miles per hour (mph) 1): 1 mph = 1.609344 km/h.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| value | Miles per hour (mph) | The amount in miles per hour to convert. |
| result | Kilometers per hour (km/h) | The same amount in kilometers per hour. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| value | Miles per hour (mph) | The amount in miles per hour to convert. |
| result | Kilometers per hour (km/h) | The amount in kilometers per hour. |

## Method

km/h = mph × 1.609344

## Assumptions

- 1 mile per hour = 1.609344 kilometers per hour, from the exact definitions in NIST SP 811.
- Exact on the typed decimals: at most 6 decimal places (6 significant digits below 0.0001), rounded half up; an answer of 1 billion or more shows at most 15 significant digits.

## Worked examples

1. value = 1 gives result = 1.609344. Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8.
2. value = 60 gives result = 96.56064. Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8.
3. result = 96.56064 gives value = 60. Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8.

## FAQ

### How many kilometers per hour are in a mile per hour?

1 mile per hour is 1.609344 kilometers per hour, from the exact unit definitions (NIST SP 811).

### How do I convert mph to km/h?

Multiply by 1.609344: km/h = mph × 1.609344. For example, 1 mph × 1.609344 = 1.609344 km/h.

### How do I convert km/h back to mph?

Multiply by 0.621371, or type the kilometers per hour into the second box and the converter works it out. 1 kilometer per hour is 0.621371 miles per hour.

### What is 60 mph in km/h?

96.56064 km/h: 60 × 1.609344. 65 mph is 104.60736 km/h, and 70 mph is 112.65408 km/h.

### Why multiply by 1.609344?

A mile is exactly 1.609344 km: 5,280 feet of 0.3048 m (NIST). Both speeds count per hour, so mph × 1.609344 = km/h.

## Sources

- NIST SP 811 (2008), Guide for the Use of the International System of Units, Appendix B.8: Factors for Units Listed Alphabetically (bold factors are exact), retrieved 2026-10-18. https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b8
- NIST, U.S. Survey Foot: Revised Unit Conversion Factors: 1 acre = 43,560 ft² = 4,046.856 422 4 m² and 1 mile = 5,280 ft = 1,609.344 m, exact with the international foot, retrieved 2026-10-18. https://www.nist.gov/pml/us-surveyfoot/revised-unit-conversion-factors