Speed Unit Converter – Check All 33 Units

Type a number in the Convert from field and pick its unit from the list below the field, then pick the unit you want under Convert to. The result appears as you type. It works the other way round too: type a number in the Convert to field and the converter fills in the first one.

Both lists hold the same 33 units in 8 groups: Most used, Metric (SI), Metric per minute, hour and day, Imperial and US customary, Nautical and aviation, Running, swimming and rowing pace, Physics and astronomy, Unusual. You don't have to look for a unit in the list. Type it with the number, for example “70 mph”, “100 kph”, “25 kt” or “Mach 0.85”, and the converter sets the unit next to the field and tells you below it which one it chose.

Type a running pace the way your watch shows it: “8:30”, “8'30"” or “8 min 30 s”. In a field set to another unit, such as mph, the converter reads this as minutes per mile, and it shows results in a pace unit as minutes and seconds.

When the Mach number is set at either field, the Air temperature for the Mach number field appears below the fields, because the speed of sound depends on temperature. It starts at 15 °C (59 °F) and takes degrees Celsius from −90 to 60.

Below the result, the converter also gives the force on the Beaufort scale, that is, how strong a wind at this speed would be. Pace units don't get this line. The Copy result button copies the number from the Convert to field, and Clear all empties both fields.

Miles per hour (mph) is the speed unit of the United Kingdom, the United States and a number of smaller countries[1]. A mile is exactly 1,609.344 m, so 1 mph is exactly 1.609344 km/h[2], and 1 km/h is about 0.621371 mph. To go from mph to km/h in your head, multiply by 1.6, and to go back, multiply by 0.62. Single pairs with their own tables are in the mph to km/h converter and the km/h to mph converter.

Meters per second show how far you travel in each second. A car at 70 mph covers about 31.3 m every second, and at 30 mph about 13.4 m. In feet, 60 mph is exactly 88 ft/s, because a mile has 5,280 feet and an hour 3,600 seconds.

All units of this group come from the foot (0.3048 m), the inch (2.54 cm), the yard (0.9144 m) and the mile[2]. The foot per second (ft/s, also written fps) is exactly 1.09728 km/h or about 0.681818 mph. In machining, US shops give cutting speed in surface feet per minute (SFM) and feed rate in inches per minute (ipm)[3], which is why the list has the foot per minute and the inch per minute. It also has the foot per hour, the foot per day, the inch per second, the inch per hour, the yard per second, the mile per minute and the mile per second.

A kilometer has 1,000 meters and an hour 3,600 seconds, so 1 m/s is exactly 3.6 km/h, and 1 km/h is about 0.277778 m/s. Multiply m/s by 3.6 to get km/h, and divide km/h by 3.6 to get m/s. A wind of 10 m/s blows at exactly 36 km/h, or about 22.4 mph.

The meter per second is the SI unit of speed, and the list also has the millimeter per second, the centimeter per second and the kilometer per second. The minute, the hour and the day are not SI units, but the International Bureau of Weights and Measures lists them among the units accepted for use with the SI[4]. That is why the meter per minute, the millimeter per minute, the kilometer per minute, the millimeter per hour and the meter per day sit next to km/h. Metric machining gives cutting speed in meters per minute and milling feed in millimeters per minute[3]: a feed of 600 mm/min is 10 mm/s.

Rain rate is measured in millimeters per hour, or in inches per hour in countries where imperial units are more common[5], and 1 in/h is exactly 25.4 mm/h. Hydrogeologists give hydraulic conductivity, which shows how easily water seeps through soil or rock, in units such as meters per day or feet per day[6].

A knot is one nautical mile per hour, exactly 1.852 km/h or about 1.15078 mph. It is used in meteorology and in maritime and air navigation. The ISO symbol is kn, while kt is common too, especially in aviation, where the International Civil Aviation Organization recommends it[7]. The converter reads kn, kt and kts. The length of the nautical mile, 1,852 m, was set by an international hydrographic conference in 1929[4], and the US adopted it in 1954, after using its own nautical mile of 1,853.248 m[7].

The name comes from the chip log, which measured a ship's speed until the mid-19th century. Sailors let a line with knots tied 47 feet 3 inches apart run out over the stern and counted the knots that passed through their fingers while a 28-second sandglass ran[7]. That spacing over 28 seconds is about 0.514 m/s, almost exactly one knot as defined today.

The admiralty knot is based on the British Admiralty mile of 6,080 feet, which Britain used until 1970[8]. It is about 1.85318 km/h, less than a thousandth faster than today's knot. The US knot follows that older US nautical mile and is exactly 1.853248 km/h.

The Mach number is the ratio of a speed to the local speed of sound, so it has no unit. It is named after the Austrian physicist Ernst Mach, after a proposal by the aeronautical engineer Jakob Ackeret in 1929[9]. At Mach 1 an aircraft flies at the speed of sound, and at Mach 1.35 it is 35% faster than sound[9], so the converter keeps the Mach number in the list with the units.

The speed of sound in air depends on temperature[9]. The converter calculates it with the formula and constants of the 1976 US Standard Atmosphere[10]. At 15 °C (59 °F), the standard temperature at sea level, it is about 340.294 m/s, so Mach 1 is about 761.216 mph or 1,225.06 km/h. Between 11 and 20 km of altitude the standard atmosphere stays at −56.5 °C (−69.7 °F)[10], and there Mach 1 is only about 660.052 mph. The often quoted 343 m/s, or about 767 mph, is the speed of sound at 20 °C (68 °F)[11], and for that temperature the converter gives 767.792 mph.

If you know the temperature at flight altitude, type it in the Air temperature for the Mach number field in degrees Celsius. The line below the fields then gives the speed of sound the converter uses.

Pace tells you how many minutes you need for a mile or a kilometer, so it is speed turned upside down: the faster you run, the smaller the number. Divide 60 by your pace in minutes to get mph. A pace of 8:00 per mile is 7.5 mph, and 6 mph on a treadmill is a pace of 10:00 min/mi.

A marathon is 42.195 km, about 26.22 miles[12], so at 8:00 per mile it takes 3:29:45. If a race or a training plan gives pace per kilometer, convert it with the minute per kilometer (running pace): 8:00 per mile is about 4:58 per kilometer.

Swimmers time themselves per 100 meters or per 100 yards. On a rowing machine, the standard measure of speed is the split, the time in minutes and seconds needed to cover 500 m[13]. A split of 2:00 is 15 km/h or about 9.321 mph.

The Beaufort scale describes wind strength in forces from 0 to 12. The converter works out the force from the speed in meters per second, using the limits of the World Meteorological Organization (WMO): force 1 starts at 0.3 m/s, force 5 at 8.0 m/s and force 12 at 32.7 m/s[14]. The limits have one decimal place, so the converter rounds the speed to 0.1 m/s and gives the force and its name below the result. The names come from the WMO table, though the Met Office calls force 9 a severe gale instead of a strong gale[15]. A wind of 30 mph is about 13.411 m/s, or 13.4 when rounded, so the converter shows the line “Wind at this speed is force 6 on the Beaufort scale: strong breeze” below the result.

Tables in knots, such as the Met Office one, set their own limits in whole knots, for example force 5 from 17 knots[15], so at the edge of a force they can give the neighboring one: 16 knots is about 8.23 m/s, which the converter counts as force 5, while the Met Office table still has it as force 4. The km/h column of the WMO table gives whole kilometers per hour and can differ in the same way: 12 km/h is about 3.33 m/s, which the converter counts as force 2, while the WMO table already lists 12 km/h under force 3[14].

The speed of light in vacuum (c) is exactly 299,792,458 m/s, or 299,792.458 km/s. The number is exact because in 1983 the meter was defined as the distance light travels in a vacuum in 1/299,792,458 of a second[16]. In miles per hour that is about 670.6 million mph.

The astronomical unit per day is one astronomical unit, exactly 149,597,870,700 m[4], covered in a day. It is about 1,731.46 km/s.

The furlong per fortnight is a joke unit from the furlong–firkin–fortnight system. It is about 0.1663 mm/s, almost exactly one centimeter per minute: the two differ by less than one part in four hundred[17].