Comparison

MPH vs KPH

Speed in miles per hour vs kilometers per hour.

	MPH (miles/hour)	KPH (km/hour)
1 mph	= 1 mph	≈ 1.609 kph
60 mph	60 mph	≈ 96.6 kph
100 kph	≈ 62.1 mph	100 kph
Used in	US, UK	Most of world

MPH (miles/hour) pros

Default on US road signs and dashboards

KPH (km/hour) pros

Default everywhere else; cleaner math with metric distance

When to use which

Use MPH (miles/hour)

Use MPH in US/UK driving contexts.

Use KPH (km/hour)

Use KPH for everything else — and for fitness tracking with metric distance.

Historical context

The two units diverge only because the mile and the kilometre do. The mile descends from the Roman mille passus, a thousand paces, and settled at 1,760 yards under an English statute of 1593. The kilometre came out of the French metric reform of the 1790s, defined against a fraction of the Earth's meridian. Since the 1959 agreement fixed the yard at exactly 0.9144 metres, one mile per hour is exactly 1.609344 kilometres per hour, which means the conversion is exact rather than approximate. The split in road signage is now unusually lopsided: the United States, the United Kingdom and a handful of smaller territories post speed limits in miles per hour, and essentially every other country uses kilometres per hour. Aviation and shipping sidestep the argument entirely by using knots, which are nautical miles per hour and tied to minutes of latitude.

Practical recommendation

Match whichever unit is on the road signs where the number will be used — this is one case where local convention wins outright, because a speed limit is a legal figure and not a preference. For rough mental conversion, multiplying by 1.6 or dividing by 1.6 is close enough for driving: 70 mph is 112.65 km/h and 130 km/h is 80.78 mph. Take particular care when hiring a car abroad, since a dashboard calibrated in the other unit is a common and expensive way to misjudge a limit.