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.

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.

When is this conversion used?

Converting between kilometre per second and mile per hour 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 kilometre per second = 2,236.93629205 mile per hour

1 mile per hour = 0.44704 metre per second

How to convert kilometre per second to mile per hour

To convert kilometre per second to mile per hour, multiply the value by 2,236.93629205.

To convert mile per hour back to kilometre per second, multiply by 0.00044704.

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: kilometre per second to mile per hour

kilometre per second	mile per hour
0.1	223.69362921
0.5	1,118.46814603
1	2,236.93629205
2	4,473.87258411
5	11,184.68146027
10	22,369.36292054
25	55,923.40730136
50	111,846.81460272
100	223,693.62920544
250	559,234.0730136
500	1,118,468.1460272
1,000	2,236,936.2920544

Common values

	kilometre per second	mile per hour
Walking speed	0.0014 kilometre per second	3.13171081 mile per hour
City speed limit	0.0139 kilometre per second	31.09341446 mile per hour
Highway driving	0.0313 kilometre per second	70.01610594 mile per hour
Commercial aircraft	0.25 kilometre per second	559.23407301 mile per hour
Speed of sound (sea level)	0.34029 kilometre per second	761.20705082 mile per hour

Available Speed units

More kilometre per second conversions

Assumption: Mach uses an approximate sea-level reference (about 340.29 m/s).