Speed Converter

You enter one number and the page gives the speed in every unit at once.

1. Type the speed in the Value box, for example 60.
2. Choose its unit in From, such as Miles per hour (mph), and the unit you want in To, such as Kilometres per hour (km/h). The result updates as you type.
3. Read the line under the result, which gives one unit in terms of the other in both directions.
4. Press Swap units to convert the opposite way without retyping.
5. Use the In every unit list to read the same speed in m/s, km/h, mph, knots, ft/s and Mach.

It helps with foreign speed limits, wind speeds in a marine forecast, aircraft and ship speeds quoted in knots, and physics problems in metres per second. Nothing is uploaded; the page works locally. Results show up to four decimals between 1 and 1,000, so check the full factor in the section below if you need more digits.

Speed is distance over time, so each factor follows from the length definitions. The converter stores every unit as metres per second and works through that base.

• 1 mph = 1.609344 km/h = 0.44704 m/s = 1.4667 ft/s
• 1 km/h = 0.2778 m/s = 0.6214 mph
• 1 knot = 1 nautical mile per hour = 1.852 km/h = 0.5144 m/s = 1.1508 mph
• 1 ft/s = 0.3048 m/s
• Mach 1 = 343 m/s = 1,234.8 km/h = 767.2691 mph = 666.7387 knots

Mach is the exception, because it is a ratio to the local speed of sound, and that depends on temperature and altitude. The tool fixes Mach 1 at 343 m/s, the speed of sound in dry air at about 20 °C, and labels it Mach (sea level). The International Standard Atmosphere at 15 °C gives a slightly lower 340.3 m/s, and at a cruising altitude of around 11 km the figure falls to about 295 m/s. For aircraft Mach numbers at altitude, treat the result as a rough guide only.

These examples use the factors above. The converter shows them rounded to four decimals, so a result such as 96.56064 appears as 96.5606.

• Road limits: 30 mph is 48.2803 km/h, 60 mph is 96.5606 km/h, 70 mph is 112.6541 km/h, and 100 km/h is 62.1371 mph.
• Walking at 5 km/h is 1.3889 m/s or 3.1069 mph.
• A sprinter at 12.4 m/s is 44.64 km/h or 27.738 mph.
• Marine: 10 knots is 18.52 km/h or 11.5078 mph, and a 40 knot wind is 74.08 km/h.
• Aviation: 900 km/h is 485.9611 knots or 559.2341 mph.
• Mach 2 is 686 m/s, 2,469.6 km/h or 1,534.5383 mph.

Two quick conversions are worth remembering. Kilometres per hour to metres per second means dividing by 3.6, since an hour has 3,600 seconds and a kilometre 1,000 metres, so 90 km/h is 25 m/s. Miles per hour to kilometres per hour means multiplying by about 1.6, which is accurate enough for reading road signs.

The list contains six units of speed, and it does not handle pace, which runners quote as minutes per kilometre or mile. Pace is the inverse of speed, so it needs a different calculation. For that, the running pace calculator turns a distance and time into pace and speed, and a finish-time table. It also does not give a distance or a duration. If you need the distance from a speed and a time, convert the units first with the length converter and the time converter, then multiply. A journey of 150 miles at 60 mph, for example, takes 2.5 hours, and the same trip is about 241.4 km at 96.56 km/h.

Speed limits and speedometer readings are exact, but real journeys are not. A 100 km/h average over 250 km takes 2.5 hours only if you never slow down, and a speedometer can read slightly high. The scientific calculator can do the arithmetic for a trip, for example 250 / 100, on a single line.