# Miles per hour to kilometers per hour converter

> Convert miles per hour to kilometers per hour (mph to km/h) with the exact factor, a conversion chart and worked steps.

Interactive version: https://www.calcopenly.com/conversion/mph-to-kmh
Subject: Unit converters

A speed in miles per hour may come from a vehicle display or a road sign. Converting the displayed speed is useful when comparing it with a metric scale. It does not change the posted limit or account for speedometer error and changing road conditions.

One mile per hour is exactly 1.609344 kilometers per hour, so 60 mph is 96.56064 km/h. To convert mph to km/h, multiply by 1.609344; to convert back, multiply by 0.6213711922.

One mile per hour is exactly 0.44704 m/s. Because both units are defined exactly, the factor above is exact and the results here carry no conversion error.

## Inputs

- **Miles per hour (mph)**

## Results

- Kilometers per hour (km/h) — main result
- Conversion
- 1 km/h in miles per hour (mph)

## Formula

$$
\text{kilometers per hour} = \text{miles per hour} \times 1.609344
$$

## Worked examples

### 60 mph to km/h

- Miles per hour (mph): 60 mph
- **Kilometers per hour: 96.56064 km/h**
- Checked against: Exact-fraction computation from the legal unit definitions (scripts/gen-pairs.py, Python fractions)

### 40 mph to km/h

- Miles per hour (mph): 40 mph
- **Kilometers per hour: 64.37376 km/h**
- Checked against: Exact-fraction computation from the legal unit definitions (scripts/gen-pairs.py, Python fractions)

### 80 mph to km/h

- Miles per hour (mph): 80 mph
- **Kilometers per hour: 128.74752 km/h**
- Checked against: Exact-fraction computation from the legal unit definitions (scripts/gen-pairs.py, Python fractions)

## Questions

### When would I convert mph to km/h?

A speed in miles per hour may come from a vehicle display or a road sign. Converting the displayed speed is useful when comparing it with a metric scale. It does not change the posted limit or account for speedometer error and changing road conditions.

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

One mile per hour is exactly 1.609344 kilometers per hour. One mile per hour is exactly 0.44704 m/s.

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

Multiply the number of miles per hour by 1.609344. For example, 60 mph × 1.609344 = 96.56064 km/h. To go the other way, divide by 1.609344.

### How can I estimate mph to km/h without a calculator?

Multiply by 1.6. That is 0.6% low of the exact factor 1.609344, so 60 mph comes out as 96 km/h instead of 96.5606.

### How accurate is the miles per hour to kilometers per hour converter?

Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 3 worked examples whose answers come from independent sources; for example, “60 mph to km/h” is checked against Exact-fraction computation from the legal unit definitions (scripts/gen-pairs.py, Python fractions).

### Where does the method come from?

NIST SP 811 (2008), Guide for the Use of the International System of Units, Appendix B; NIST Handbook 44, Appendix C: General tables of units of measurement; BIPM, The International System of Units (SI Brochure), 9th edition.

## Sources

- [NIST SP 811 (2008), Guide for the Use of the International System of Units, Appendix B](https://www.nist.gov/pml/special-publication-811)
- [NIST Handbook 44, Appendix C: General tables of units of measurement](https://www.nist.gov/pml/weights-and-measures/publications/nist-handbooks/handbook-44)
- [BIPM, The International System of Units (SI Brochure), 9th edition](https://www.bipm.org/en/publications/si-brochure)