Light-seconds to Kilometers (ls to km)

1 light-second equals 299,792.458 kilometers exactly.

1 light-second = 299,792.458 kilometers

How to convert light-seconds to kilometers

To convert light-seconds to kilometers, multiply the number of light-seconds by 299,792.458. This factor is exact. To go the other way, multiply kilometers by 0.000003335640952 (rounded).

kilometers = light-seconds × 299,792.458

Example: 10 light-seconds = 2,997,924.58 kilometers.

About these units

Light-second (ls)

AstronomicalCurrent unit

The distance light travels in a vacuum in one second: 299,792,458 meters. The Moon is about 1.28 light-seconds from Earth.

Because the speed of light is now fixed at 299,792,458 meters per second, a light-second is exactly that many meters, with no uncertainty at all. Astronomers and radio engineers treat it as a convenient yardstick for distances that are small on the scale of the solar system but large on the scale of a laboratory. The abbreviation ls appears in tables of astronomical units, and it is not an official SI unit.

The Moon is the standard example: its average distance from Earth is about 1.282 light-seconds, which is why a radio exchange with a lunar mission has a noticeable round-trip lag of roughly two and a half seconds. The Earth's mean diameter is only about 0.0425 light-seconds, while the Sun's diameter is about 4.643. One astronomical unit is about 499 light-seconds. Sixty light-seconds make a light-minute, 3,600 make a light-hour, and 31,557,600 make a light-year, based on the Julian year.

1 light-second = 299,792,458 meters (exactly).

Sources: Wikipedia: Light-second; Wikipedia: Light-minute

Kilometer (km)

Metric (SI)Current unit

1,000 meters. The standard unit for road distances in most countries.

A name for 1,000 meters took a while to settle. In 1793 France's National Convention made the metre the sole French unit of length, and the first proposed name for the thousand-metre multiple was millaire. Everyday French usage then leaned on the myriametre, 10,000 meters, well into the 1800s. The Netherlands adopted the kilometre in 1817, under the local name mijl, and made it the only official unit of that size in 1867. In 1935 the CIPM dropped the myria- prefix, which left the kilometre as the standard unit for road-scale distances.

Kilo- is the SI prefix for a thousand, and the kilometre is now the preferred unit for land distances in most of the world, with the United States, the United Kingdom and Liberia among those that still use the mile. One kilometre is about 0.621 mile. The main span of Lisbon's 25 de Abril Bridge, at 1.013 km, gives a sense of the scale. Even its pronunciation has been argued over: in 1970 Australia's Metric Conversion Board made stress on the first syllable official, although Prime Minister Gough Whitlam argued for stress on the second. Military slang in several countries calls it a klick.

1 kilometer = 1,000 meters (exactly).

Sources: Wikipedia: Kilometre; Wikipedia: Metric prefix; BIPM: history of the metre

Related conversions

See all length units.