Speed Converter

Multiply miles per hour by 1.609344 to get kilometers per hour. For example, 60 mph × 1.609 = 96.56 km/h. For a quick estimate, multiply by 1.6 or add 60% to mph. US speed limit of 65 mph ≈ 105 km/h.

Multiply kilometers per hour by 0.621371 to get miles per hour. For example, 100 km/h × 0.621 = 62.1 mph. For a quick estimate, multiply by 0.6 or take 60% of km/h. European highway speed of 130 km/h ≈ 81 mph.

A knot equals 1 nautical mile per hour, which is 1.151 mph or 1.852 km/h. Knots are used in aviation and maritime because nautical miles relate directly to latitude and longitude: 1 nautical mile = 1 minute of arc of latitude. This makes navigation calculations simpler.

Mach number is the ratio of an object's speed to the speed of sound. Mach 1 is the speed of sound, approximately 767 mph (1,235 km/h) at sea level and 59°F. The exact speed varies with air temperature and pressure. Mach 2 is twice the speed of sound. The SR-71 Blackbird flew at Mach 3.3.

The speed of light in a vacuum is exactly 299,792,458 meters per second (about 186,282 miles per second or 670,616,629 mph). It's the fastest speed possible in the universe. Light travels from the Sun to Earth in about 8 minutes.

US highway: 65-75 mph = 105-121 km/h. US residential: 25 mph = 40 km/h. European highway: 120-130 km/h = 75-81 mph. German Autobahn advisory: 130 km/h = 81 mph (no limit on some sections). UK motorway: 70 mph = 113 km/h.

Multiply m/s by 3.6 to get km/h, or divide m/s by 0.278. For example, 10 m/s × 3.6 = 36 km/h. This works because there are 3,600 seconds in an hour and 1,000 meters in a kilometer: (3600/1000 = 3.6).

Speed is a scalar—just the magnitude of motion (e.g., 60 mph). Velocity is a vector—it includes both speed and direction (e.g., 60 mph north). In everyday use, they're often used interchangeably, but in physics, the distinction matters for calculations involving direction.