Convert between speed units quickly.
Switch between road, sea, air, and lab speeds without juggling separate calculators.
Mach in this tool is a single reference (speed of sound ≈ 295 m/s at sea level). Real engineering uses tables because sound speed shifts with temperature and altitude—use this row for rough comparison, not certification math.
Internal math uses Meter per second as the common base across all 6 units in the table.
Rough ballparks—use the calculator above for exact figures:
This page uses one approximate speed of sound in dry air at sea level (~295 m/s) so every unit stays consistent in the table. In real flight, Mach depends on temperature and altitude, so aircraft manuals and simulators use atmosphere models—not a single constant.
Knots tie directly to nautical miles per hour, so aviation and maritime traffic, weather reports, and charts standardize on knots. Road vehicles use mph or km/h; scientific work often uses m/s. Pick the unit your chart, regulator, or textbook already uses.
Yes—both are length per time. m/s is the SI-style rate you see in physics; km/h is common for vehicles. Convert carefully when mixing with imperial mph or with knots, which are not the same numeric scale as mph.
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Browse all toolsType the speed number. Decimals are supported (e.g. 9.58 for Usain Bolt's 100m record average speed).
Choose from: miles per hour (mph), kilometres per hour (km/h), metres per second (m/s), feet per second (ft/s), or knots (kn).
All speed equivalents update instantly. A context note shows where this speed falls relative to familiar references (walking pace, highway speed, sound speed).
Input
70 mph (UK motorway limit)Output
112.7 km/h · 31.3 m/sThe UK uses mph; continental Europe uses km/h. A 70 mph motorway limit equals 112.7 km/h. This is why a UK driver in France should look for the 110–130 km/h highway limit signs.
Input
9.58 m/s (sprint)Output
34.5 km/h · 21.4 mph · 31.4 ft/sUsain Bolt's average speed during his 9.58s 100m world record was 10.44 m/s (his top speed was ~12.4 m/s = 44.7 km/h = 27.8 mph).
Common real-world scenarios where this tool saves time.
International drivers and road trippers
Rental car GPS units display speed in different units than local road signs depending on country settings. Convert mph to km/h to stay compliant with local speed limits.
Physics and engineering students
Physics equations use SI units (m/s), but everyday speeds are given in km/h or mph. Convert readings to m/s before plugging into kinematic equations.
Sailors and pilots
Marine speeds use knots (nautical miles per hour). 1 knot = 1.852 km/h = 1.151 mph. Weather reports for maritime use quote wind speed in knots; the same wind in km/h helps compare with land weather.
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Multiply mph by 1.60934. Common values: 30 mph = 48.3 km/h, 60 mph = 96.6 km/h, 70 mph = 112.7 km/h, 100 mph = 160.9 km/h. Quick approximation: multiply mph by 1.6.
Multiply km/h by 0.62137. Common values: 50 km/h = 31.1 mph, 80 km/h = 49.7 mph, 100 km/h = 62.1 mph, 130 km/h = 80.8 mph. Quick approximation: multiply km/h by 0.6.
1 knot = 1 nautical mile per hour = 1.852 km/h = 1.151 mph. Knots are the standard speed unit in marine and aviation contexts. A ship cruising at 20 knots is travelling at 37 km/h.
Multiply m/s by 3.6. This is exact: 1 m/s = 3600 m/hour = 3.6 km/h. Example: 10 m/s = 36 km/h, sprint speed of 10 m/s ≈ 36 km/h ≈ 22.4 mph.
Speed of sound in air (at 20°C, sea level): 343 m/s = 1235 km/h = 767 mph = 667 knots. Mach 1 = speed of sound; Mach 2 = twice the speed of sound. The exact value varies with air temperature and altitude.
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Reviewed by EverydayTools Editorial Team.