Speed Converter - km/h, mph, m/s, Knots & ft/s

About the Speed Converter

Speeds are quoted in different units depending on who is measuring. Road signs use kilometres per hour in most of the world but miles per hour in the US and UK. Scientists use metres per second. Ships, aircraft and weather reports use knots, and engineers in the US sometimes use feet per second. A runner may think in pace — minutes per kilometre or per mile — rather than speed at all.

This speed converter converts between km/h, mph, metres per second, knots and feet per second. It shows the result, the exact factor both ways and the speed in every other unit. For walking, running and cycling speeds it adds the pace per kilometre and per mile; for faster speeds it shows how long 100 km and 100 miles take. It also gives the speed as a Mach number, a fraction of the speed of sound.

How to Use the Speed Converter

Enter the speed.

Choose the unit to convert from and to.

The result appears with the factor, the speed in all five units, and pace or travel time.

How Speed Conversion Works

Each speed unit is a distance per time, and each has an exact value in metres per second:

  1 km/h  = 1,000 m ÷ 3,600 s   = 0.277778 m/s   (divide by 3.6)
  1 mph   = 1,609.344 m ÷ 3,600 s = 0.44704 m/s
  1 knot  = 1,852 m ÷ 3,600 s   = 0.514444 m/s
  1 ft/s  = 0.3048 m/s

  result = value × (from-unit in m/s) ÷ (to-unit in m/s)
  pace (min per km) = 60 ÷ speed in km/h

Step-by-Step Example

100 km/h to mph.

  To m/s:    100 ÷ 3.6 = 27.7778 m/s
  To mph:    27.7778 ÷ 0.44704 = 62.1371 mph

So 100 km/h is about 62.1371 mph. At that speed, 100 km takes exactly one hour, and 100 miles about 1 hour 37 minutes.

60 mph to km/h is 60 × 1.609344 = 96.5606 km/h, which is also exactly 88 feet per second.

A running speed of 12 km/h is a pace of 60 ÷ 12 = 5:00 per kilometre, or about 8:03 per mile, so a 10 km run takes 50 minutes.

Quick Reference

  1 km/h  = 0.621371 mph      1 mph  = 1.609344 km/h
  1 m/s   = 3.6 km/h          1 m/s  = 2.23694 mph
  1 knot  = 1.852 km/h        1 knot = 1.15078 mph
  30 mph  = 48.2803 km/h      50 km/h = 31.0686 mph
  70 mph  = 112.654 km/h      120 km/h = 74.5645 mph

A quick mental conversion is to multiply mph by 1.6 for km/h, or km/h by 5/8 for mph. Both are within about 1 percent.

Pace and Speed

Runners and walkers usually think in pace, the time taken for each kilometre or mile, rather than speed. Pace is simply the inverse of speed: 60 divided by the speed in km/h gives minutes per kilometre. A walking speed of 5 km/h is a pace of 12 minutes per kilometre; a steady jog at 10 km/h is 6 minutes per kilometre. Because the relationship is inverse, small speed increases save less and less time at higher speeds.

Knots at Sea and in the Air

The knot is based on the nautical mile, originally one minute of latitude, which made it convenient for navigation with charts. It is still used for ships' speeds, aircraft airspeeds and wind speeds in marine and aviation forecasts. A container ship might cruise at 20 knots, 37.04 km/h; an airliner at around 450 knots, about 833 km/h.

Mach Number

The Mach number compares a speed with the speed of sound, which in air at 20 °C is about 343 metres per second, or 1,235 km/h. The speed of sound falls in colder air, so at the height where airliners cruise, where the air is far below freezing, Mach 1 is nearer 1,062 km/h. The converter uses the 20 °C figure as a simple guide.

Speed Limits and Stopping Distances

Speed limits are set in whole numbers in each country's own unit, so converted limits come out awkward: 50 km/h is about 31 mph, 80 km/h about 50 mph and 130 km/h, a common motorway limit in Europe, about 81 mph. Hire cars abroad often show both scales on the speedometer, but the smaller numbers can be hard to read at a glance.

Converting to metres or feet per second shows why speed matters so much for safety. At 100 km/h a car covers almost 28 metres every second, so a typical reaction time of about 1.5 seconds uses up more than 40 metres before the brakes are even applied. At 60 mph, 88 feet go by every second.

Understanding Your Result

The headline is the converted speed.

The conversion factor shows the exact factor both ways.

The in every unit line gives the speed in all five units.

The also line gives pace per kilometre and mile for speeds under 30 km/h, or the time for 100 km and 100 miles for faster ones.

The worth knowing line gives the speed as a fraction of the speed of sound.

When Should You Use This Calculator?

Use it when driving abroad, to understand speed limits in the other unit.

Use it for running, walking and cycling pace.

Use it for physics homework, where speeds must be in metres per second.

Use it for sailing, flying and wind speeds given in knots.

Common Mistakes

Dividing by 3.6 the wrong way. km/h to m/s divides by 3.6; m/s to km/h multiplies.

Treating a knot as a mile per hour. A knot is about 15 percent faster.

Averaging paces directly. Average speed over a distance comes from total distance ÷ total time.

Rounding mph to km/h as 1.5. Use 1.6, or the exact 1.609344.

Mixing time units. A speed in metres per minute or kilometres per second needs converting to one of the listed units first.

Confusing speed and velocity. Velocity includes direction; the converter works with the size of the speed.