Speed Converter
km/h · mph · m/s · Knots · Mach
Enter a speed and select units to convert.
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Speed Quick Reference
To convert km/h to mph, divide by 1.609344 or multiply by 0.621371, so 100 km/h = 62.14 mph. The factor is exact because the international mile is defined as 1,609.344 meters. Enter a value above and the converter shows it in km/h, mph, m/s, knots, feet per second, Mach and the speed of light at the same time.
Common speed conversions and real-world reference points.
| Reference | km/h | mph | m/s |
|---|---|---|---|
| Walking pace | 5 | 3.1 | 1.39 |
| City speed limit | 50 | 31.1 | 13.9 |
| Motorway limit (UK) | 113 | 70 | 31.3 |
| Autobahn advisory speed (DE) | 130 | 80.8 | 36.1 |
| Cruising airliner | 900 | 559 | 250 |
| Speed of sound (20°C air) | 1,235 | 767 | 343 |
Mach 1 in the standard atmosphere at sea level (15°C) = 1,225 km/h (761 mph, 340.3 m/s). Speed of sound varies with temperature and altitude. 1 knot = 1 nautical mile per hour = 1.852 km/h.
Exact Speed Conversion Factors
Every factor below except Mach is exact by definition, so the converter uses the full values and only rounds the display.
| 1 unit | m/s | km/h | mph | Why |
|---|---|---|---|---|
| 1 km/h | 0.277778 | 1 | 0.621371 | 1,000 m in 3,600 s (exact) |
| 1 mph | 0.44704 | 1.609344 | 1 | 1 mile = 1,609.344 m (exact) |
| 1 knot | 0.514444 | 1.852 | 1.150779 | 1 nautical mile = 1,852 m (exact) |
| 1 ft/s | 0.3048 | 1.09728 | 0.681818 | 1 ft = 0.3048 m (exact) |
| 1 m/s | 1 | 3.6 | 2.236936 | SI base unit |
| Mach 1 | 340.294 | 1,225.06 | 761.22 | Standard atmosphere, sea level, 15°C |
| Speed of light | 299,792,458 | 1,079,252,849 | 670,616,629 | Exact, defines the meter |
Road Speeds mph to km/h
US speed limits converted exactly, with meters and feet per second for stopping distance math.
| mph | km/h | m/s | ft/s |
|---|---|---|---|
| 25 | 40.2 | 11.18 | 36.7 |
| 30 | 48.3 | 13.41 | 44.0 |
| 35 | 56.3 | 15.65 | 51.3 |
| 45 | 72.4 | 20.12 | 66.0 |
| 55 | 88.5 | 24.59 | 80.7 |
| 60 | 96.6 | 26.82 | 88.0 |
| 65 | 104.6 | 29.06 | 95.3 |
| 70 | 112.7 | 31.29 | 102.7 |
| 75 | 120.7 | 33.53 | 110.0 |
| 80 | 128.7 | 35.76 | 117.3 |
60 mph is exactly 88 feet per second. At that speed a car covers 132 feet in a 1.5 second reaction time, before the brakes do anything.
Mach 1 Depends on Air Temperature
Mach is a ratio, not a fixed speed: Mach 1 is the local speed of sound, which in dry air depends only on temperature. The converter uses the standard sea-level value of 340.294 m/s at 15°C (59°F).
| Air temperature | m/s | km/h | mph | knots |
|---|---|---|---|---|
| −56.5°C (−69.7°F), airliner cruise at 11 km | 295.1 | 1,062 | 660 | 574 |
| −20°C (−4°F) | 319.0 | 1,148 | 713 | 620 |
| 0°C (32°F) | 331.3 | 1,193 | 741 | 644 |
| 15°C (59°F), standard sea level | 340.3 | 1,225 | 761 | 661 |
| 20°C (68°F) | 343.2 | 1,236 | 768 | 667 |
| 30°C (86°F) | 349.0 | 1,257 | 781 | 678 |
That is why an airliner at Mach 0.85 in the cold air at 11 km is doing about 903 km/h (561 mph) through the air, while Mach 0.85 at sea level would be about 1,041 km/h.
Shortcuts and Common Mistakes
- km/h to mph: multiply by 5, divide by 8. The result is 0.6% high (100 km/h gives 62.5 instead of 62.1).
- mph to km/h: multiply by 1.6. The result is 0.6% low (60 mph gives 96 instead of 96.6).
- m/s to km/h: multiply by 3.6. This one is exact.
- knots to mph: add 15%. 20 knots is about 23 mph.
- m/s to mph: multiply by 2.24. A 10 m/s wind is about 22 mph.
Mistakes to avoid
- Treating knots and mph as the same. A knot is 15% faster, which matters for boat and aircraft speeds.
- Saying "knots per hour". A knot is already a speed (one nautical mile per hour).
- Using one fixed value for Mach at every altitude. See the table above.
- Confusing ft/s (feet per second) with fps as frames per second in video.
Method and sources. Length definitions from NIST Special Publication 811 and NIST Handbook 44: 1 international mile = 1,609.344 m, 1 foot = 0.3048 m and 1 nautical mile = 1,852 m, all exact, with 1 hour = 3,600 s. The speed of light, 299,792,458 m/s, is exact under the SI definition of the meter. Speed of sound computed as the square root of γRT for dry air with γ = 1.4 and R = 287.05 J/(kg·K); 340.294 m/s is the International Standard Atmosphere sea-level value. Every number in the tables was computed with these factors.
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Speed Conversion Questions
Multiply km/h by 0.621371 to get mph. Example: 100 km/h = 62.14 mph. To go the other way, multiply mph by 1.60934. Quick mental trick: multiply by 5 and divide by 8 (e.g. 80 km/h × 5 ÷ 8 = 50 mph). Common conversions: 50 km/h = 31.1 mph · 100 km/h = 62.1 mph · 120 km/h = 74.6 mph.
One knot = 1.852 km/h = 1.151 mph = 0.5144 m/s. A knot is one nautical mile per hour. It is used in aviation and maritime navigation because nautical miles correspond to degrees of latitude. A ship travelling at 20 knots is moving at 37 km/h (23 mph). Cruising speed for a large container ship is about 20 to 25 knots.
Mach 1 at sea level and 15°C = 1,225 km/h (761 mph, 340.3 m/s). The speed of sound varies with temperature and altitude: at cruising altitude (−57°C), it is about 1,062 km/h (660 mph). A commercial jet cruises at roughly Mach 0.85 (900 km/h). The Concorde cruised at Mach 2.04 (2,179 km/h).
Multiply m/s by 3.6 to get km/h. Example: 10 m/s = 36 km/h. To convert km/h to m/s, divide by 3.6. This is because 1 km/h = 1000 m / 3600 s = 1/3.6 m/s. Physics problems typically use m/s; road signs use km/h or mph; weather wind speeds often use m/s or knots.
The speed of light in a vacuum is exactly 299,792,458 m/s = 1,079,252,849 km/h = 670,616,629 mph. It is defined as a physical constant and is used to define the meter. Nothing with mass can reach the speed of light. Light takes about 8 minutes 20 seconds to travel from the Sun to the Earth.
Common motorway speed limits: UK: 70 mph (113 km/h) · USA: typically 65 to 80 mph (105 to 129 km/h) · Germany (Autobahn): advisory 130 km/h (81 mph), no general limit on unrestricted sections · France: 130 km/h (81 mph) · Australia: 110 km/h (68 mph). Urban limits are typically 50 km/h (31 mph) or 30 mph (48 km/h).
Commercial jets cruise at approximately 850 to 950 km/h (530 to 590 mph), typically around Mach 0.82 to 0.85. This is the ground speed in still air; actual ground speed varies with wind (jet streams can add 150 km/h tailwind). Take-off speed is about 260 to 290 km/h (160 to 180 mph) and landing speed about 240 to 260 km/h (150 to 160 mph).
Usain Bolt's world record 100m sprint peak speed: 44.72 km/h (27.8 mph). Average recreational runner: 8 to 12 km/h (5 to 7.5 mph). Marathon world record pace: about 21 km/h (13 mph). Walking pace: 4 to 6 km/h (2.5 to 3.7 mph). The average person cannot sustain more than 15 to 20 km/h for more than a few seconds.
Feet per second (ft/s or fps) is used in US ballistics, firearms, and some engineering contexts. 1 ft/s = 0.3048 m/s = 1.09728 km/h = 0.6818 mph. Bullet velocities are typically 300 to 1,000 m/s (980 to 3,280 fps). The muzzle velocity of a typical 9mm handgun is about 370 m/s (1,214 fps). fps is also used in athletics for sprint analysis.
The Beaufort scale classifies wind by effect: Force 0 (calm, 0 km/h) to Force 12 (hurricane, 118+ km/h). A gentle breeze (Force 3) = 12 to 19 km/h (7 to 12 mph). Gale (Force 8) = 62 to 74 km/h (39 to 46 mph). Hurricane (Force 12) = 118+ km/h (73+ mph). The Saffir-Simpson scale classifies hurricanes: Category 1 starts at 119 km/h (74 mph), Category 5 exceeds 252 km/h (157 mph).
Yes, by about 15%. 1 knot = 1.1508 mph because a nautical mile (1,852 m) is longer than a statute mile (1,609.344 m). So 20 knots is 23.0 mph and 100 knots is 115.1 mph. A knot already means per hour, so "knots per hour" is not a speed.
Multiply mph by 22/15, about 1.4667, because a mile is 5,280 feet and an hour is 3,600 seconds. 30 mph is exactly 44 ft/s, 45 mph is 66 ft/s and 60 mph is 88 ft/s. To go back, multiply ft/s by 15/22 (0.6818).