Speed Converter

Convert between all common units of speed: kilometers per hour, miles per hour, meters per second, knots and feet per second. Enter a speed, pick the source and target unit, and get the exact result instantly. Below the converter you can also read where each unit comes from, why ships and planes still measure in knots, and what typical speeds look like in all four units.

Speed conversion

Convertinto=–

All units at a glance

Enter a speed to see all conversions.

Typical speeds compared

A feeling for the numbers helps more than any formula. This table shows a few everyday and not so everyday speeds in all four common units, converted with the same exact factors the calculator above uses.

Example	km/h	mph	kn	m/s
Brisk walking	5	3.1	2.7	1.4
Relaxed cycling	20	12.4	10.8	5.6
City speed limit	50	31.1	27	13.9
Motorway pace	130	80.8	70.2	36.1
Container ship	44.4	27.6	24	12.3
High-speed train (ICE, TGV)	300	186.4	162	83.3
Airliner at cruise	907.5	563.9	490	252.1
Sound in air at 20 °C	1,234.8	767.3	666.7	343

Where the units come from

Kilometers per hour and miles per hour are the two big road units. The mile goes back to Roman times, but the version used today, the statute mile of 5,280 feet, was fixed by the English Parliament in 1593. The kilometer is much younger: the meter was created during the French Revolution in the 1790s and was originally defined as one ten millionth of the distance from the North Pole to the equator. As railways and cars spread in the 19th and 20th centuries, km/h became the standard on road signs almost everywhere, while the United States and the United Kingdom kept mph.

Meters per second is the scientific unit of speed in the SI system and the yardstick all the others are defined against: 1 m/s is exactly 3.6 km/h. Physics, engineering and weather services prefer m/s because it fits meters and seconds without any conversion factor. Wind speeds in scientific reports are usually given in m/s for exactly that reason.

The knot is one nautical mile per hour, exactly 1.852 km/h, and it is the standard unit at sea and in aviation. Feet per second appears mostly in American engineering tables and in ballistics. How the knot got its unusual name is a story of its own, told below.

How the knot was invented

Before electronics, sailors had no speedometer. From the late 16th century they used a surprisingly clever tool called the chip log: a wooden board on a long rope, thrown over the stern of the ship. The board stayed roughly in place in the water while the ship sailed on and the rope ran out through a sailor's hands. The first printed description of the method appeared in William Bourne's book A Regiment for the Sea in 1574.

The rope had knots tied into it at regular distances, in the standardized version every 47 feet and 3 inches, which is about 14.4 meters. A shipmate turned a small sandglass that ran for 28 seconds. The sailor holding the rope simply counted how many knots slipped through his fingers before the sand ran out. That count was the speed: five knots counted meant the ship was making five nautical miles per hour.

The trick is in the numbers: 14.4 meters in 28 seconds is almost exactly one nautical mile per hour. The tool itself disappeared long ago, replaced first by mechanical and then by electronic logs, but the counted knots live on as the name of the unit. A ship's logbook is also named after that wooden log.

Why ships and planes still use knots

The nautical mile is not an arbitrary length. It was defined as one minute of latitude, one sixtieth of a degree, measured along a meridian. That ties the unit directly to the coordinate grid printed on every nautical chart: one minute of latitude on the chart is one nautical mile on the water. A navigator can take distances straight off the chart's latitude scale with a pair of dividers, and a speed in knots says immediately how many minutes of latitude the ship covers in an hour.

Because the Earth is slightly flattened, a real minute of latitude varies between about 1,843 meters at the equator and 1,862 meters at the poles. The First International Extraordinary Hydrographic Conference in Monaco settled on a compromise in 1929 and defined the international nautical mile as exactly 1,852 meters. The United States adopted that definition in 1954 and the United Kingdom in 1970.

Aviation inherited the whole system. Aircraft navigate on the same grid of latitude and longitude as ships, so aeronautical charts, flight plans, wind reports and air traffic control all work in nautical miles and knots. When the international rules of civil aviation were agreed after 1944, the ICAO kept the knot as a standard unit, and it has stayed that way worldwide. Marine weather forecasts give wind speeds in knots for the same reason.

Quick rules of thumb

From km/h to m/s, divide by 3.6; back the other way, multiply by 3.6. So 90 km/h is exactly 25 m/s.
From mph to km/h, multiply by 1.6 (the exact factor is 1.609344). 60 mph is a little under 100 km/h.
From knots to km/h, double the number and take away about 7 percent (the exact factor is 1.852). 20 knots is about 37 km/h.
Knots and mph are close neighbours: 1 knot is about 1.15 mph, so 100 knots is roughly 115 mph.

Frequently asked questions

Is a knot faster than a mile per hour?

Yes. One knot is one nautical mile per hour, which is exactly 1.852 km/h or about 1.151 mph. A ship doing 20 knots is therefore moving at about 23 mph or 37 km/h.

Why does dividing by 3.6 turn km/h into m/s?

A kilometer is 1,000 meters and an hour is 3,600 seconds. So 1 km/h equals 1000 divided by 3600 meters per second, which is 1/3.6 m/s. Every factor in this calculator works the same way: it is simply the ratio of the two unit definitions.

How fast is Mach 1?

Mach 1 is the speed of sound, and it is not a fixed number: it depends on the air temperature. At 20 °C near the ground, sound travels at about 343 m/s, which is 1,235 km/h or 667 knots. In the cold air at airliner cruising altitude it drops to about 295 m/s, roughly 1,060 km/h. That is why aircraft speeds near the sound barrier are given as a Mach number instead of a fixed value.

What is the difference between a nautical mile and a normal mile?

The statute mile used on roads in the US and the UK measures 1,609.344 meters and goes back to an English law of 1593. The nautical mile measures 1,852 meters and comes from geography: it was defined as one minute of latitude. That is also why there is no simple round factor between mph and knots.