Conversion from Kilometers to Nautical miles

Information about the Kilometer (km)

The kilometre is one thousand metres, written km. It is the standard unit for road distance, geographic separation and travel across almost the entire world, and after the metre itself it is the most widely used SI length unit.

Road signs, speed limits, vehicle odometers and navigation systems use it in every country except the United States, Liberia and Myanmar, where miles remain in place. The United Kingdom occupies a middle position: road signs and speed limits are in miles, while most other official measurement is metric. Running and cycling events are almost universally set in kilometres, with the marathon a notable exception at 42.195 km, a distance fixed by the route used at the 1908 London Olympics rather than by any round figure.

The unit suits the human scale of travel. A brisk walk covers about five kilometres in an hour. Urban journeys are typically a few kilometres, and national distances run to hundreds or thousands. Below one kilometre metres are more natural, and above a few thousand many people switch to comparing flight times instead.

Pronunciation is contested. The stress pattern KIL-o-metre follows the pattern of other SI prefixed units such as kilogram and kilowatt, where the prefix is unstressed. The alternative, ki-LOM-eter, is nonetheless dominant in North America and common in Australia and New Zealand, and both are recorded as standard by major dictionaries.

The kilometre also anchors two other units. A square kilometre is one million square metres, or 100 hectares, and is the usual measure for the area of towns, lakes and protected land. Speed is expressed as kilometres per hour, written km/h.

Astronomy uses the kilometre for objects within the solar system, where larger units would be unwieldy. The Moon averages 384,400 km from Earth and the Sun about 149.6 million km. Beyond that distance astronomers switch to astronomical units, light years and parsecs, because the kilometre figures become too long to read. Orbital velocities are given in kilometres per second: the International Space Station travels at roughly 7.66 km/s.

One kilometre equals 1000 metres or 100,000 centimetres. It is approximately 0.621371 miles, so a five-kilometre race is a little over three miles.

Information about the Nautical mile (nmi)

The nautical mile is a unit of length equal to exactly 1852 metres. The symbol is nmi, though NM and M also appear in maritime and aviation practice. It is longer than the statute mile by about 15 per cent.

Its definition is geographical rather than arbitrary. One nautical mile corresponds to one minute of latitude, so sixty nautical miles span one degree. This makes navigation on a chart remarkably direct: a navigator can measure a distance against the latitude scale printed on the chart's edge without any conversion, because the two are the same thing. No other length unit has this property, which is why the nautical mile has resisted metrication where almost every other traditional unit has given way.

Because the Earth is slightly flattened, a minute of latitude is not constant, varying from about 1843 metres at the equator to 1862 metres at the poles. The First International Extraordinary Hydrographic Conference in Monaco adopted the round figure of 1852 metres in 1929 to settle the discrepancy. The United States accepted this value in 1954 and the United Kingdom in 1970, both having previously used slightly different definitions.

Speed at sea and in the air is measured in knots, one knot being one nautical mile per hour. The name records the method: a log line knotted at regular intervals was paid out behind a ship and the knots counted against a sand glass. Aviation adopted both units from maritime practice, and aircraft airspeed indicators worldwide read in knots.

Maritime law is written in the same unit. Territorial waters extend twelve nautical miles from the baseline and exclusive economic zones two hundred, figures set by the United Nations Convention on the Law of the Sea.

A related unit occasionally appears in older texts. The geographical mile is one minute of arc along the equator, about 1855 metres, and differs slightly from the nautical mile because it is measured on a great circle rather than a meridian. The distinction rarely matters in practice but explains small discrepancies between historical sources.

One nautical mile equals 1852 metres, about 1.15078 statute miles, or 6076.12 feet.