Speed Unit Converter
Convert speeds between mph, km/h, m/s, knots, Mach, and the speed of light. Instant all-unit conversion with reference speeds.
Convert Speed
Reference Speeds
| Reference | km/h | mph | m/s |
|---|---|---|---|
| Walking | 5.04 | 3.131711 | 1.4 |
| Cycling | 21.6 | 13.421618 | 6 |
| City speed limit (50 km/h) | 50.004 | 31.071045 | 13.89 |
| Highway speed limit (100 km/h) | 100.008 | 62.14209 | 27.78 |
| Fastest land vehicle | 1,227.96 | 763.01897 | 341.1 |
| Speed of sound (sea level) | 1,225.044 | 761.20705 | 340.29 |
| Commercial jet (cruising) | 900 | 559.23407 | 250 |
| SR-71 Blackbird (Mach 3.3) | 4,032 | 2,505.3686 | 1,120 |
| Space Shuttle (orbit) | 28,080 | 17,448.103 | 7,800 |
| Speed of light | 1,079,252,800 | 670,616,630 | 299,792,460 |
How to Use Speed Unit Converter
- 1Enter a speed value in any unit.
- 2All other units convert instantly.
- 3Compare to reference speeds like sound and light.
- 4Copy any converted value.
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Frequently Asked Questions
What is the difference between mph and km/h?▾
1 mph = 1.60934 km/h. Common conversions: 60 mph = 96.6 km/h, 100 km/h = 62.1 mph, 30 mph = 48.3 km/h. The US uses mph for road speeds; most other countries use km/h. The EU requires speed limits in km/h. UK road signs use mph despite being metric in other areas. Remember: 100 km/h is roughly 60 mph.
What is a knot?▾
A knot is 1 nautical mile per hour. 1 knot = 1.852 km/h = 1.15078 mph. Knots are used in aviation and maritime navigation because nautical miles are based on latitude degrees (1 nautical mile = 1 arc-minute of latitude), making navigation calculations simpler. A commercial jet cruises at about 500-600 knots; a cargo ship at about 12-18 knots.
What is Mach number?▾
The Mach number is the ratio of an object's speed to the local speed of sound. Mach 1 = the speed of sound in the medium. At sea level at 15°C, the speed of sound is about 340 m/s (1,235 km/h, 767 mph). At cruising altitude where air is colder (~−50°C), sound travels slower: ~300 m/s. So Mach 1 for an aircraft depends on altitude. Concorde cruised at Mach 2.02.
How fast is the speed of light?▾
The speed of light in vacuum is exactly 299,792,458 m/s (about 300,000 km/s or 186,282 miles per second). This is the universal speed limit — nothing with mass can reach it. Light travels from Earth to Moon in about 1.3 seconds, Earth to Sun in 8.3 minutes, and Earth to the nearest star (Proxima Centauri) in about 4.2 years. It is denoted c in physics.
What is the difference between speed and velocity?▾
Speed is a scalar — it has magnitude only (60 mph). Velocity is a vector — it has magnitude and direction (60 mph north). In physics, average speed = total distance / time; average velocity = displacement / time. A car driving in a circle at constant speed has changing velocity (direction changes). Speedometers measure speed; GPS navigation uses velocity vectors.