Convert miles per hour to kilometres per hour

One mile per hour is 1.609344 kilometres per hour. To convert any amount, multiply by 1.609344. Going the other way, one kilometre per hour is 0.621371192 miles per hour.

Multiply the mile per hour figure by 1.609344. So km/h = mph × 1.609344. For a quick mental estimate, multiplying by about 1.61 gets you within a percent or so, which is close enough for most everyday purposes.

One mile per hour is 60 mph is a typical highway speed. Miles per hour is the road-speed unit in the United States and the United Kingdom, and in both it is what appears on the speedometer regardless of what the road signs say elsewhere.

One kilometre per hour is 100 km/h is a typical highway limit. Kilometres per hour is the speed-limit unit in every country except the US, the UK and a few small territories.

Yes. Since the 1959 international yard and pound agreement, the imperial and metric systems are related by exact definitions rather than measurements — the inch is exactly 25.4 mm and the pound exactly 0.45359237 kg. Everything derived from those, including this conversion, is therefore exact. Round at the end rather than partway through, since rounding mph before converting introduces an error the conversion then multiplies.