# How to convert miles to km?

Converts miles (mi) to kilometers (km) and back, with the exact unit definitions.

- Page: https://www.acalculator.org/convert/miles-to-km
- JSON spec: https://www.acalculator.org/convert/miles-to-km.json
- Version: f4de5d752cf4

## Default answer

Example with the default inputs (Miles (mi) 1): 1 mi = 1.609344 km.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| value | Miles (mi) | The amount in miles to convert. |
| result | Kilometers (km) | The same amount in kilometers. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| value | Miles (mi) | The amount in miles to convert. |
| result | Kilometers (km) | The amount in kilometers. |

## Method

km = mi × 1.609344

## Assumptions

- 1 mile = 1.609344 kilometers, 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 = 26.2 gives result = 42.164813. Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8.
3. result = 42.164813 gives value = 26.2. Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8.

## FAQ

### How many kilometers are in a mile?

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

### How do I convert miles to km?

Multiply by 1.609344: km = mi × 1.609344. For example, 1 mi × 1.609344 = 1.609344 km.

### How do I convert km back to miles?

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

### What is 26.2 miles in km?

42.164813 km: 26.2 × 1.609344.

### Why multiply by 1.609344?

A mile is exactly 1.609344 km: 5,280 feet of 0.3048 m (NIST).

## 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