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From: Kilometers per Hour (km/h)
To: Miles per Hour (mph)
Speed is the measure of how quickly an object moves from one place to another. Different systems and contexts use different units to measure speed, from everyday travel speeds to scientific applications.
The metric system uses meters per second (m/s) as the base unit for speed, with kilometers per hour (km/h) being more common in everyday contexts like road speed limits in most countries outside the United States.
| Unit | Symbol | Equivalent to |
|---|---|---|
| Meters per second | m/s | 1 m/s = 3.6 km/h |
| Kilometers per hour | km/h | 1 km/h = 0.2778 m/s |
| Kilometers per second | km/s | 1 km/s = 1000 m/s |
Road speed limits (km/h), physics calculations (m/s), scientific measurements
In the United States and some other countries, imperial units are used for measuring speed. Miles per hour (mph) is the standard unit for road speeds in the US and the UK.
| Unit | Symbol | Equivalent to |
|---|---|---|
| Miles per hour | mph | 1 mph = 1.6093 km/h |
| Feet per second | ft/s | 1 ft/s = 0.3048 m/s |
| Inches per second | in/s | 1 in/s = 0.0254 m/s |
Road speed limits in US/UK (mph), engineering applications (ft/s), sports (mph)
1 knot = 1 nautical mile per hour = 1.852 km/h = 0.5144 m/s
Used in maritime navigation, aviation, and meteorology to measure boat speed, aircraft speed, and wind speed.
The term "knot" comes from sailors using a piece of wood tied to a rope with knots at regular intervals, which was thrown overboard to measure ship speed.
Ratio of an object's speed to the speed of sound in the surrounding medium
At sea level and 15°C, Mach 1 ≈ 340.29 m/s ≈ 1,225 km/h ≈ 761.2 mph
Named after Austrian physicist Ernst Mach, this unit is used primarily in aerospace engineering and supersonic flight. Aircraft traveling faster than Mach 1 are supersonic, while those over Mach 5 are hypersonic.
The universal physical constant
c = 299,792,458 m/s (exactly) ≈ 1.079 × 10⁹ km/h ≈ 670,616,629 mph
In physics, the speed of light in a vacuum is the ultimate speed limit in the universe. According to Einstein's theory of relativity, no matter or information can travel faster than this speed.
| To Convert | To | Multiply By |
|---|---|---|
| Kilometers per hour (km/h) | Miles per hour (mph) | 0.6214 |
| Miles per hour (mph) | Kilometers per hour (km/h) | 1.6093 |
| Meters per second (m/s) | Kilometers per hour (km/h) | 3.6 |
| Feet per second (ft/s) | Meters per second (m/s) | 0.3048 |
| Knots (kn) | Kilometers per hour (km/h) | 1.852 |
Value₂ = Value₁ × (Factor₁ ÷ Factor₂)
Where Factor₁ is the conversion factor of the original unit to the base unit (m/s), and Factor₂ is the conversion factor of the target unit to the base unit.
1. mph to m/s factor: 0.44704
2. km/h to m/s factor: 0.27778
3. Calculate: 60 mph × (0.44704 ÷ 0.27778) = 60 × 1.6093 = 96.558 km/h
• 100 km/h ≈ 62 mph (multiply by 0.62)
• 60 mph ≈ 97 km/h (multiply by 1.61)
• 1 m/s ≈ 3.6 km/h (multiply by 3.6)
• 1 knot ≈ 1.15 mph (multiply by 1.15)
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| Object/Phenomenon | Approximate Speed |
|---|---|
| Walking pace | 5 km/h (3.1 mph) |
| Running (sprinting) | 36 km/h (22.4 mph) |
| Highway speed limit | 100 km/h (62 mph) |
| Commercial jet aircraft | 900 km/h (559 mph) |
| Sound in air (sea level) | 1,235 km/h (767 mph) |
| Space shuttle (orbit) | 28,000 km/h (17,400 mph) |
| Light in a vacuum | 1.08 × 10⁹ km/h (6.7 × 10⁸ mph) |