What is mile per hour?
Mile per hour is a unit of speed equal to one mile travelled in one hour. It is the standard unit for road speeds, vehicle performance ratings, and weather reports in the United States and United Kingdom.
Real-world uses
Miles per hour is the standard speed unit for road traffic in the United States, the United Kingdom, and a few other countries. Baseball pitching speed, hurricane wind categories (Saffir-Simpson scale), and NASCAR race speeds are quoted in mph.
History
Miles per hour became the standard speed expression in English-speaking countries with the advent of railways and later automobiles. The first US speed limit (8 mph in New York City, 1901) and British speed cameras use mph as the legal standard.
Common mistakes
Assuming mph-to-km/h conversion is a simple ×1.5—the actual factor is 1.609. Also, forgetting that UK and US speed limits both use mph, which can mislead visitors from metric countries into driving too fast or too slow.
What is kilometre per second?
Kilometre per second is a unit of speed equal to 1,000 metres per second. It is used in astrophysics, rocket propulsion, and the measurement of planetary and cosmic velocities.
Real-world uses
Kilometres per second is used in astronomy and astrophysics for orbital velocities, galaxy recession speeds, and asteroid approach velocities. Earth orbits the Sun at about 29.78 km/s, and escape velocity from Earth is about 11.2 km/s.
History
Kilometres per second became a standard unit in celestial mechanics and astrophysics during the 20th century. It provides convenient numbers for solar system velocities, while larger cosmic speeds are often expressed as fractions of the speed of light.
Common mistakes
Forgetting the enormous scale—1 km/s = 3,600 km/h. A common error is treating km/s figures as if they were km/h. Also, confusing orbital speed with escape velocity, which are related but different concepts.
When is this conversion used?
Converting between mile per hour and kilometre per second is common when working across metric and imperial systems, such as international trade, travel between countries with different measurement standards, or following instructions from a different region. Speed limits, vehicle speedometers, and weather reports for wind speeds use different units depending on the country, making km/h to mph conversion one of the most practical speed conversions.
Worked examples
1 mile per hour = 0.00044704 kilometre per second
1 kilometre per second = 1,000 metre per second
How to convert mile per hour to kilometre per second
To convert mile per hour to kilometre per second, multiply the value by 0.00044704.
To convert kilometre per second back to mile per hour, multiply by 2,236.93629205.
Measurement standards
The SI unit of speed is metres per second (m/s), a derived unit requiring no independent definition. The knot is defined as exactly one nautical mile (1,852 metres) per hour and is sanctioned for maritime and aeronautical navigation by the International Civil Aviation Organization.
Did you know?
The fastest human-made object is the Parker Solar Probe, which reached 635,266 km/h (about 176 km/s) in 2024 during a close pass of the Sun — fast enough to travel from New York to Tokyo in under a minute.
Quick reference: mile per hour to kilometre per second
| mile per hour | kilometre per second |
|---|---|
| 0.1 | 0.0000447 |
| 0.5 | 0.00022352 |
| 1 | 0.00044704 |
| 2 | 0.00089408 |
| 5 | 0.0022352 |
| 10 | 0.0044704 |
| 25 | 0.011176 |
| 50 | 0.022352 |
| 100 | 0.044704 |
| 250 | 0.11176 |
| 500 | 0.22352 |
| 1,000 | 0.44704 |
Common values
| mile per hour | kilometre per second | |
|---|---|---|
| Walking speed | 3.13171081 mile per hour | 0.0014 kilometre per second |
| City speed limit | 31.09341446 mile per hour | 0.0139 kilometre per second |
| Highway driving | 70.01610594 mile per hour | 0.0313 kilometre per second |
| Commercial aircraft | 559.23407301 mile per hour | 0.25 kilometre per second |
| Speed of sound (sea level) | 761.20705082 mile per hour | 0.34029 kilometre per second |
Available Speed units
More mile per hour conversions
- Convert mile per hour to metre per second
- Convert mile per hour to kilometre per hour
- Convert mile per hour to knot
- Convert mile per hour to foot per second
- Convert mile per hour to metre per minute
- Convert mile per hour to kilometre per second
- Convert mile per hour to mach (approx at sea level)
- Convert mile per hour to centimetre per second
- Convert mile per hour to mile per minute
Assumption: Mach uses an approximate sea-level reference (about 340.29 m/s).