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 foot per second?

Foot per second is a unit of speed in imperial and US customary systems. It is used in ballistics, sports science, and engineering calculations that rely on US customary units.

Real-world uses

Feet per second is used in ballistics for bullet muzzle velocities (e.g., 2,800 fps for a rifle round), aerospace engineering for aircraft approach speeds, and fluid dynamics in American engineering contexts. Elevator speeds are sometimes specified in ft/s.

History

Feet per second has been used in English-language engineering since the 18th century, particularly in artillery and ballistics. It remains the standard velocity unit in American firearms and aerospace industries despite the broader shift toward metric units.

Common mistakes

Confusing feet per second with miles per hour. 1 ft/s ≈ 0.682 mph, so they are quite different. Also, using fps as an abbreviation for both "feet per second" and "frames per second" creates ambiguity in technical documents.

When is this conversion used?

Converting between kilometre per second and foot 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.

Worked examples

1 kilometre per second = 3,280.83989501 foot per second

1 foot per second = 0.3048 metre per second

How to convert kilometre per second to foot per second

To convert kilometre per second to foot per second, multiply the value by 3,280.83989501.

To convert foot per second back to kilometre per second, multiply by 0.0003048.

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 foot per second

kilometre per second	foot per second
0.1	328.0839895
0.5	1,640.41994751
1	3,280.83989501
2	6,561.67979003
5	16,404.19947507
10	32,808.39895013
25	82,020.99737533
50	164,041.99475066
100	328,083.98950131
250	820,209.97375328
500	1,640,419.94750656
1,000	3,280,839.89501312

Common values

	kilometre per second	foot per second
Walking speed	0.0014 kilometre per second	4.59317585 foot per second
City speed limit	0.0139 kilometre per second	45.60367454 foot per second
Highway driving	0.0313 kilometre per second	102.69028871 foot per second
Commercial aircraft	0.25 kilometre per second	820.20997375 foot per second
Speed of sound (sea level)	0.34029 kilometre per second	1,116.43700787 foot per second

Available Speed units

More kilometre per second conversions

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