🏎️ Mph to Kmh Converter
Convert miles per hour to kilometres per hour and back. The exact factor, a table of the values people look up most, and what each unit is actually used for.
Converting miles per hour to kilometres per hour
One mile per hour is 1.609344 kilometres per hour, and one kilometre per hour is 0.6213711922 miles per hour.
kilometres per hour = miles per hour × 1.609344
Getting the precision right
The factor is the same 1.609344 as for distance, since speed is just distance over a shared unit of time. The common slip is converting a limit and then treating the result as a posted limit: 70 mph is 112.65 km/h, and the nearest real posted limit is 110 or 120 depending on the country.
Where each unit is used
Road speeds are posted in mph in the United States and the United Kingdom, and in km/h almost everywhere else. Car speedometers sold in either market usually show both, with the secondary scale in smaller figures on the inner ring.
Values worth knowing
| mph | km/h |
|---|---|
| 10 | 16.0934 |
| 20 | 32.1869 |
| 30 | 48.2803 |
| 40 | 64.3738 |
| 50 | 80.4672 |
| 60 | 96.5606 |
| 70 | 112.654 |
| 80 | 128.748 |
| 100 | 160.934 |
| 120 | 193.121 |
30 mph is 48 km/h, the typical urban limit. 70 mph is 113 km/h. 100 km/h is 62 mph. Usain Bolt's peak was about 27 mph, or 44 km/h.
Where the two units came from
Speed limits followed whichever distance unit the country already used for its road signs, which is why the division is so clean: miles in the United States and United Kingdom, kilometres almost everywhere else. Canada switched in 1977 over a single weekend, replacing signs nationwide, and the UK considered doing the same in the 1990s but abandoned it on cost. Vehicle speedometers are legally allowed to read high but never low in most jurisdictions, so the dial typically overstates by a few percent.
Round the result to the precision your own work needs. These converters carry the full factor, which is useful for checking but rarely what you want to write down.
Two neighbours worth knowing: the sq ft to sq m, for the question this one leads into, and the acres to hectares, which answers it from the other direction.
Frequently Asked Questions (FAQs)
How do I convert mph to km/h?
Multiply by 1.609344. For a quick estimate, add 60% to the mph figure: 50 mph becomes 80 km/h, which is accurate to within a percent.
What is 70 mph in km/h?
112.65 km/h. UK motorway limits of 70 mph are therefore slightly below the 120 km/h common on European motorways and slightly above the 110 used in some countries.
Do speedometers show both?
Most do, with one scale printed inside the other. Speedometers are also permitted to read slightly high by law in many countries, so an indicated 70 may be an actual 67, which is why GPS speed often reads lower than the dial.