mph to km/h Calculator - Miles per Hour to km/h

About the mph to km/h Calculator

Road speeds in the United States and the United Kingdom are posted in miles per hour, while almost every other country uses kilometres per hour. Driving abroad, reading a car review from another market, comparing top speeds, or working through a physics problem all mean turning mph into km/h — and getting it right matters on the road, where a misread speed limit can mean a fine or worse.

This mph to km/h calculator converts miles per hour to kilometres per hour exactly. It also shows the speed in metres per second and feet per second, the distance covered in one second and during a typical reaction time, and how long a mile and a kilometre take at that speed.

How to Use the mph to km/h Calculator

Enter the speed in mph.

The km/h figure appears straight away, together with metres and feet per second, the distance per second and the time per mile and per kilometre.

The Formula

  km/h = mph × 1.609344
  m/s  = mph × 0.44704
  ft/s = mph × 5,280 ÷ 3,600  (= mph × 1.46667)

The factor 1.609344 is exact, because a mile is exactly 1.609344 kilometres. The same factor works for any speed, from a walking pace to an aircraft's.

Step-by-Step Example

60 mph.

  km/h:  60 × 1.609344 = 96.5606 km/h
  m/s:   60 × 0.44704 = 26.8224 m/s
  ft/s:  60 × 1.46667 = 88 ft/s

At 60 mph a car covers 26.8 metres every second. A mile takes exactly one minute, and a kilometre about 37.3 seconds.

70 mph, the UK motorway limit, is 112.654 km/h, or 31.3 metres per second.

Speed Limits Compared

These are the limits drivers meet most often, converted in both directions:

  20 mph  =  32.2 km/h        30 km/h  =  18.6 mph
  30 mph  =  48.3 km/h        50 km/h  =  31.1 mph
  40 mph  =  64.4 km/h        80 km/h  =  49.7 mph
  50 mph  =  80.5 km/h        100 km/h =  62.1 mph
  60 mph  =  96.6 km/h        120 km/h =  74.6 mph
  70 mph  = 112.7 km/h        130 km/h =  80.8 mph

Limits in each system are set in round numbers, so converted limits rarely match exactly. A 50 km/h town limit is a little faster than 30 mph; a 130 km/h motorway limit is a little over 80 mph.

Quick Mental Conversions

Multiply mph by 1.6 for a quick km/h figure: 50 × 1.6 = 80 km/h, against the exact 80.47. Or add 60 percent: 40 mph plus 24 is 64 km/h. Both are within about half a percent — close enough for reading signs, though for a hire car it is simplest to switch the display to the local unit if the car allows it.

Speed and Stopping Distance

Converting speed into metres per second shows why speed matters so much. At 30 mph a car covers about 13.4 m every second; at 70 mph, about 31.3 m. Before the brakes even begin to work, a driver's reaction time of around 1.5 seconds uses up 20 m at 30 mph and nearly 47 m at 70 mph. Braking distance then grows with the square of the speed, so doubling the speed roughly quadruples it.

Beyond the Road

The same conversion applies to wind speeds in weather reports, athletes' speeds and aircraft. A 100 mph wind is about 161 km/h; the fastest sprinters reach around 27 mph, about 44 km/h; a fastball in baseball at 100 mph is also about 161 km/h. For boats and aircraft, speeds are usually given in knots, which need their own conversion.

Hire Cars and Dual Speedometers

Cars sold in mph countries usually have a speedometer with a large mph scale and a small km/h scale, and the reverse elsewhere. When driving a hire car abroad, the small inner scale is hard to read at a glance, so many drivers prefer to switch the digital display to the local unit or to learn the handful of converted limits they will meet: 50 km/h in towns is about 31 mph, 90 km/h on country roads about 56 mph, and 130 km/h on motorways about 81 mph. Speed cameras enforce the local limit in the local unit, so it is worth knowing both figures before setting off.

Acceleration Figures

Car makers in Europe quote acceleration as 0 to 100 km/h, while American and British figures use 0 to 60 mph. Since 100 km/h is 62.1 mph, the European figure is a little slower for the same car — typically by a few tenths of a second — so the two cannot be compared directly without allowing for the extra 2 mph.

Understanding Your Result

The headline is the speed in km/h.

The metres per second line gives the speed in m/s and ft/s.

The distance each second line shows how far you travel in one second and in a 1.5-second reaction time.

The time per mile and km line shows how long each distance takes at that speed.

When Should You Use This Calculator?

Use it when driving abroad or reading foreign speed limits.

Use it to compare car specifications, top speeds and acceleration figures.

Use it for wind speeds and sports speeds given in mph.

Use it for physics problems that need metres per second.

Common Mistakes

Dividing instead of multiplying. From mph to km/h, multiply by 1.609344.

Rounding the factor to 1.5. That is nearly 7 percent low.

Confusing mph with knots. A knot is about 15 percent faster than 1 mph, and is used for boats, aircraft and marine winds.

Treating km/h and kph as different. They are the same unit, written two ways.

Forgetting speedometers read slightly high. The true speed is often a little lower than the dial shows, by design.

Using the wrong limit abroad. Signs are always in the local unit.