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 knot?

A knot is a unit of speed equal to one nautical mile per hour, approximately 1.852 km/h. It is the international standard for maritime navigation, aviation, and meteorological wind speed reporting.

Real-world uses

Knots are the universal speed unit in maritime navigation and aviation worldwide, regardless of whether a country uses metric or imperial. Ship speeds, ocean currents, wind speed in aviation weather (METAR) reports, and jet stream velocities are all given in knots.

History

The knot originates from the 17th-century practice of measuring ship speed by throwing a log overboard attached to a rope with knots tied at regular intervals. Sailors counted how many knots paid out in a fixed time (measured by a sandglass).

Common mistakes

Saying "knots per hour"—a knot already means nautical miles per hour, so adding "per hour" is redundant and incorrect. Also, confusing knots with km/h: 1 knot ≈ 1.852 km/h.

When is this conversion used?

Converting between kilometre per second and knot 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 = 1,943.84449261 knot

1 knot = 0.51444444 metre per second

How to convert kilometre per second to knot

To convert kilometre per second to knot, multiply the value by 1,943.84449261.

To convert knot back to kilometre per second, multiply by 0.00051444.

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 knot

kilometre per second	knot
0.1	194.38444926
0.5	971.9222463
1	1,943.84449261
2	3,887.68898522
5	9,719.22246304
10	19,438.44492609
25	48,596.11231521
50	97,192.22463043
100	194,384.44926085
250	485,961.12315213
500	971,922.24630427
1,000	1,943,844.49260854

Common values

	kilometre per second	knot
Walking speed	0.0014 kilometre per second	2.72138229 knot
City speed limit	0.0139 kilometre per second	27.01943845 knot
Highway driving	0.0313 kilometre per second	60.84233262 knot
Commercial aircraft	0.25 kilometre per second	485.96112315 knot
Speed of sound (sea level)	0.34029 kilometre per second	661.47084239 knot

Available Speed units

More kilometre per second conversions

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