Speed Converter: Kmh to Mph, Knots, m/s, ft/s and Mach

How to use this tool

Type a speed, pick the unit it is in and the unit you want. The answer appears in the dark panel and, underneath it, the same speed in all six units plus the two running paces, so a question like how fast is 20 knots in mph, km/h and m/s is answered at once. Tap any card to copy its value. Swap reverses the two units, and the decimal places control applies everywhere.

Three notes sit under the cards. The green one shows the factor and where it comes from. The amber one appears for km/h and mph only and answers the question people actually have when driving abroad: if you round to the nearest number a sign would show in the other system, are you over or under the real limit. The blue one reads the speed as a wind and gives its Beaufort force, which is the quickest way to make sense of a marine forecast in knots.

The input people most often get wrong is the knot. It is not a metric unit and it is not the same as mph. A knot is one nautical mile per hour, and the nautical mile is 1,852 metres, longer than the statute mile, so a speed in knots is always about 15 percent bigger in mph. Pick Knots from the list rather than typing a knot figure into a mph box.

Every export carries the speed you entered and nothing else. Copy link gives an address that reopens the converter on the same speed and units, and every chip and table row is a link with its own address too.

What the conversion is actually doing

Every speed on this page is turned into metres per second first, then into the unit you asked for. A kilometre per hour is 1000 metres in 3600 seconds, 0.2778 m/s. A mile per hour is 1,609.344 metres in 3600 seconds, 0.44704 m/s. A knot is 1,852 metres in 3600 seconds, 0.5144 m/s. A foot per second is 0.3048 m/s. Dividing one of these by another gives the factor between the two units, and that is the whole calculation.

What makes the factors worth trusting is that none of them is a measurement. The international mile is defined as exactly 1,609.344 metres, which follows from the 1959 agreement that fixed the yard at exactly 0.9144 metres, the same treaty that fixed the pound at 0.45359237 kilograms. The nautical mile was fixed at exactly 1,852 metres in 1929. Since every unit has an exact definition, the ratio between any two of them is exact, and the conversion introduces no error of its own.

Mach is the exception. Mach 1 is the speed of sound, which depends on air temperature, so it is not a fixed unit at all. This page uses the standard atmosphere value at sea level and 15 °C, 340.294 m/s, and says so on every result that involves it. At the top of the troposphere the air is around minus 56 °C and sound travels at about 295 m/s, so an airliner at Mach 0.85 up there is doing about 900 km/h, not the 1,041 km/h the sea level figure would suggest.

The coincidence worth memorising

There is one conversion in this area that comes out perfectly clean, and it is useful. Sixty miles per hour is exactly 88 feet per second. A mile is 5,280 feet, so 60 miles is 316,800 feet, and an hour is 3,600 seconds. Divide one by the other and you get 88 with nothing left over. It works because 5,280 and 3,600 happen to share enough factors, not because anyone designed it that way.

This is why North American stopping distance tables and reaction time rules of thumb are so often built around 60 mph. At that speed a driver covers 88 feet in every second, so a reaction time of three quarters of a second is 66 feet of road gone before the brakes are even touched. The metric equivalent is less tidy: 100 km/h is 27.78 metres per second, which nobody remembers.

Knots, and why the sea and the sky use them

A nautical mile is one minute of latitude, one sixtieth of a degree, which is why charts and navigators use it: distance and angle on the globe become the same number. Speed in nautical miles per hour, knots, follows from that, and the word comes from the knotted line sailors paid out behind a ship to time its speed. Aviation inherited the whole system because aircraft navigate over the same charts.

The practical consequence is that wind and water speeds arrive in knots and everyone else thinks in km/h or mph. Twenty knots sounds mild and is a fresh breeze at 37 km/h; fifty knots sounds like a strong wind and is storm force at 93 km/h. The Beaufort readout on this page exists for exactly that gap, and the knots hub below covers every value a marine forecast is likely to use.

A worked check you can repeat on paper

Take 100 km/h. Divide by 1.609344 and you get 62.137119 mph. Round at the end, never in the middle, and you have 62.14 mph. Check it a different way: 100 km/h is 100,000 metres in 3,600 seconds, 27.7778 m/s, and one mph is 0.44704 m/s, so 27.7778 ÷ 0.44704 = 62.137 again, without ever touching the 1.609344 factor.

Now 20 knots to mph. One knot is 1,852 metres per hour and one mph is 1,609.344 metres per hour, so 1 knot is 1,852 ÷ 1,609.344 = 1.150779 mph, and 20 knots is 23.0156 mph. In km/h it is simply 20 × 1.852 = 37.04. The converter reports these figures, so if yours differ, check which mile you used.

Finally the shortcut people use for km/h to mph, multiplying by 0.6. It gives 60 mph for 100 km/h, and the real answer is 62.14, so the shortcut has quietly lost 2.14 mph. On a motorway that is the difference between sitting at the limit and being overtaken by everyone.

Mistakes that catch people out

Using 0.6 instead of 0.6214. The shortcut is short by about one part in thirty. At 100 km/h that is 2.14 mph, and at 300 km/h it is 6.4 mph. Fine for a rough sense of pace, not fine for anything you write down.

Assuming the round number in the other system is the same limit. It almost never is. A 60 mph limit is 96.56 km/h, so treating it as 100 km/h has you 3.44 km/h over. A 100 km/h limit is 62.14 mph, so treating it as 60 mph has you crawling. The chart above shows six common cases and three of them put you over.

Treating knots as mph. A knot is 1.1508 mph. A 40 knot gust is a 46 mph gust, and reading a marine forecast as mph understates it by fifteen percent every time.

Quoting Mach as a fixed speed. Mach 2 is 2,450 km/h at sea level and about 2,120 km/h at cruising altitude, because the speed of sound drops with temperature. A Mach number without an altitude is not a speed.

Trusting the speedometer to be exact. Type approval rules in the UK, the EU and elsewhere say a speedometer may never read lower than the true speed, but it is allowed to read high by a margin. Most cars are deliberately optimistic by a few percent, so converting a speedometer reading gives you a converted speedometer reading, not a converted true speed.

Rounding partway through. Converting 120 km/h to 74.6 mph and then to feet per second gives a slightly different answer from carrying 74.564543 all the way. The gap is tiny on one number and grows across a table, so round once at the end.

Popular speed conversions

The speeds people look up most. Each opens the converter ready to go and has its own address you can share.

Kilometres per hour to miles per hour

Miles per hour to kilometres per hour

Knots to mph and km/h

Wind, boat and aircraft speeds. Small craft advisories start around 20 knots, gale force at 34 knots, storm force at 48 and hurricane force at 64.

Mph and km/h to knots

Metres per second and feet per second

Mach to km/h and mph

How this was checked

The engine was written twice. The first version converts through metres per second using the exact definitions of the metre, the mile, the nautical mile and the foot. The second computes the km/h to mph factor directly as 1,609.344 ÷ 1,000 and the knot factors directly from 1,852 ÷ 1,609.344. Across the test values the two routes agree to within floating point precision, about one part in a hundred thousand billion, and a mistyped digit in either constant would show up immediately.

Round tripping was checked across every pair of the six units, all 36 combinations, converting a speed out and back; every one returned the original figure to within a billionth. The 88 feet per second identity was confirmed both from 5,280 feet divided by 3,600 seconds and through the metric route, and 100 mph came out at 86.8976 knots by both routes. The Beaufort bands use the standard metres per second thresholds, so 20 knots (10.29 m/s) lands in force 5 and 64 knots (32.9 m/s) in force 12, as the published scale has them.

Common questions

How do you convert km/h to mph?

Divide by 1.609344. 100 km/h ÷ 1.609344 = 62.14 mph. To go from mph to km/h, multiply by the same number: 60 mph × 1.609344 = 96.56 km/h. The factor is exact because a mile is defined as exactly 1,609.344 metres.

How many mph is 20 knots?

20 knots is 23.02 mph, or 37.04 km/h. A knot is one nautical mile per hour and a nautical mile is exactly 1,852 metres, so 1 knot is 1.150779 mph and 1.852 km/h. To convert knots to mph multiply by 1.1508; to convert mph to knots multiply by 0.8690.

Is a knot faster than a mile per hour?

Yes, by about 15 percent. One knot is 1.1508 mph because the nautical mile (1,852 m) is longer than the statute mile (1,609.344 m). A ship doing 30 knots is doing 34.5 mph, and a 50 knot wind is a 57.5 mph wind.

What is Mach 1 in km/h and mph?

At sea level in the standard atmosphere, 15 °C, the speed of sound is 340.294 m/s, which is 1,225.06 km/h, 761.22 mph or 661.48 knots. It falls with temperature, so at typical cruising altitude Mach 1 is about 1,062 km/h. Aircraft Mach numbers are always relative to the local speed of sound, not the sea level figure.

Why is 60 mph exactly 88 feet per second?

Because 60 miles is 316,800 feet (60 × 5,280) and an hour is 3,600 seconds, and 316,800 ÷ 3,600 is exactly 88. It is a coincidence of the two definitions rather than a design, and it is why North American stopping distance tables are built around 60 mph.

How do I turn a speed into a running pace?

Divide the distance by the speed. At 10 km/h you cover a kilometre in 6 minutes, so the pace is 6:00 per km; a mile is 1.609 km, so the same speed is 9:39 per mile. The converter shows both paces for every speed, and going the other way, a 5:00 per km pace is 12 km/h.

Related Calculators and Reference

• Fuel Economy Converter: turn these speeds and distances into fuel used, where miles per gallon turns out to be an inverse scale.
• Length and Distance Converter: the distances underneath these speeds, including the survey foot the 1959 agreement left behind.
• Kilograms to Pounds Converter: the mass side of the same 1959 agreement, where the pound was fixed at exactly 0.45359237 kg.
• Temperature Converter: the other reading that changes meaning the moment you cross a border, and the one that moves the speed of sound.
• Angle Converter: degrees and minutes, the geometry the nautical mile is built on.
• Wind Chill Calculator: wind speed in any unit turned into the wind chill.
• Speed Distance Time Calculator: travel time and average speed from a distance.
• Kinetic Energy Calculator: the energy that speed carries.
• Gear Ratio and RPM to Speed Calculator: road speed from engine RPM and gearing.
• NIST Special Publication 811: the primary reference for the exact factors used here, including the 1,609.344 metre mile and the 1,852 metre nautical mile.