Convert between all common speed units including km/h, mph, meters per second, knots, feet per second, and Mach. Instant bidirectional conversion. Runs in your browser.
Speed measurement varies by context: cars use km/h or mph, scientists prefer m/s, sailors and pilots use knots, and sound has its own unit (Mach). Converting between these units is essential for international travel, physics calculations, aviation planning, and understanding weather reports. This converter handles all common speed units with precise conversions. Key relationships: 1 mph ≈ 1.609 km/h, 1 knot ≈ 1.852 km/h, 1 m/s = 3.6 km/h, Mach 1 ≈ 343 m/s (at sea level, 20°C). The tool converts in real time as you type, showing results in every supported unit simultaneously.
Knots are nautical miles per hour. One nautical mile equals one minute of latitude, making navigation calculations on charts intuitive. At 60 knots, you cover one degree of latitude per hour. This direct relationship to Earth's geometry made it the natural choice for maritime and aviation.
Mach 1 is the speed of sound, approximately 343 m/s (1,235 km/h) at sea level and 20°C. The exact value varies with temperature and altitude. Mach 2 is twice the speed of sound. Named after physicist Ernst Mach.
Divide by 3.6. Example: 100 km/h ÷ 3.6 ≈ 27.78 m/s. Reverse: multiply m/s by 3.6 to get km/h. This is because there are 3,600 seconds in an hour and 1,000 meters in a kilometer (3600/1000 = 3.6).
In a vehicle: Apollo 10 crew reached 39,897 km/h (24,791 mph) during lunar return. On land: Thrust SSC reached 1,228 km/h (763 mph). Running: Usain Bolt's peak speed was 44.72 km/h (27.8 mph).
The US never fully adopted the metric system. While most countries switched to km/h in the 20th century, the US retained miles per hour along with other imperial units. The UK uses mph too, despite being partially metric.