Speed Of Light to Kilometers Per Hour (c to km/h)

1 speed of light equals 1,079,252,849 kilometers per hour (rounded).

1 speed of light = 1,079,252,849 kilometers per hour

How to convert speed of light to kilometers per hour

To convert speed of light to kilometers per hour, multiply the number of speed of light by 1,079,252,849. The factor is rounded to 10 significant digits. To go the other way, multiply kilometers per hour by 9.265669311×10⁻¹⁰ (rounded).

kilometers per hour = speed of light × 1,079,252,849

Example: 10 speed of light = 10,792,528,488 kilometers per hour.

About these units

Speed Of Light (c)

ScientificCurrent unit

Exactly 299,792,458 m/s, the speed of light in a vacuum and the fundamental constant that defines the meter.

Light was once thought to arrive instantly. In 1676 Ole Rømer timed eclipses of Jupiter's moon Io and concluded that light takes about 22 minutes to cross Earth's orbit. In 1729 James Bradley used the aberration of starlight to estimate about 8 minutes 12 seconds from Sun to Earth. Later experimenters used a toothed wheel (Fizeau), a rotating mirror (Foucault), and in 1930 to 1935 Michelson, Pease and Pearson used a mile-long vacuum chamber. The letter c is itself uncertain: it may stand for constant or the Latin celeritas, swiftness, and Einstein switched to it in 1907.

Since 1983 the speed of light has been fixed at exactly 299,792,458 m/s, and the meter is defined as the distance light travels in a vacuum in 1/299,792,458 of a second. Measurement therefore became a matter of defining the constant, not of improving experiments. For scale, light takes about 1.3 seconds to travel from the Earth to the Moon, about 8.3 minutes from the Sun, and roughly one nanosecond to go a foot. James Clerk Maxwell showed in 1865 that light is an electromagnetic wave.

1 speed of light = 299,792,458 meters per second (exactly).

Sources: Wikipedia: Speed of light; NIST: the meter and the SI redefinition

Kilometer Per Hour (km/h)

Metric (SI)Current unit

The standard unit for road speeds in most countries: 1 km/h is about 0.2778 m/s.

Myriameters per hour came first, at least in French. Although the meter was defined in 1799, speeds were initially quoted using the myriameter of 10,000 meters, and the phrase myriamètres par heure appears in 1802. The Dutch adopted the kilometer in 1817 under the name mijl. English abbreviations only appeared in the late nineteenth century, and many competing forms followed, from k. p. h. in 1889 to KMPH in 1940. Reuters and The Economist still prefer kph.

SI treats km/h as a unit symbol, not an abbreviation, and it is the generally preferred form. The European Union required SI usage in 1972, and a 1975 directive requires km/h on speedometers in all languages. In the United States a 1988 NHTSA rule allowed km/h on speedometers. Exactly 3.6 km/h make 1 m/s, one mile per hour is exactly 1.609344 km/h, and one knot is exactly 1.852 km/h. Road signs and speed limits in most of the world use it.

1 kilometer per hour = 0.2777777778 meters per second (approximately).

Sources: Wikipedia: Kilometres per hour; NIST Guide to the SI, Appendix B.8: conversion factors

Related conversions

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