Conversion from Centimeters to Nautical miles

Information about the Centimeter (cm)

The centimetre is one hundredth of a metre, written cm. Among the metric subdivisions it is the one people reach for most readily in daily life, occupying the range where objects are small enough to hold but too large to measure comfortably in millimetres.

Body measurement is its most common application. Height, waist, chest and inside leg are recorded in centimetres across most of the world, and clothing is sized accordingly. Paediatric growth charts plot height and head circumference in centimetres against age. Rainfall over long periods, snow depth and the dimensions of furniture and luggage are all reported the same way.

The unit had a formal role in science for nearly a century. The centimetre-gram-second system, adopted by the British Association for the Advancement of Science in 1874, took the centimetre as its base unit of length. CGS units such as the erg, the dyne and the gauss were standard in physics until the metre-kilogram-second system displaced them, and SI formally superseded CGS in 1960. Some CGS units persist in astronomy and in parts of electromagnetism.

Volume follows naturally. A cubic centimetre, written cm³ or cc, equals exactly one millilitre. Engine displacement is often quoted in cubic centimetres, particularly for motorcycles, and medical syringes are marked the same way.

Despite its usefulness, the centimetre sits awkwardly in engineering practice. Technical drawings prefer millimetres precisely to avoid mixing units that differ by a factor of ten, since a misplaced decimal point between the two is a plausible and expensive error.

Map scales often make the unit explicit. A 1:25,000 map means one centimetre on the paper represents 25,000 centimetres on the ground, or 250 metres, so four centimetres cover a kilometre. Walkers and orienteers use this relationship constantly, and it is one of the clearer illustrations of why a decimal system is convenient: converting between the two scales requires only moving a decimal point.

Two well-known wavelengths fall in this range and are named by it. Neutral hydrogen radiates at 21 centimetres, a line predicted in 1944 and detected seven years later, and because hydrogen fills the galaxy that single wavelength has mapped the spiral arms of the Milky Way and the rotation curves that first indicated dark matter. Domestic microwave ovens work at 12.2 centimetres, chosen from a band set aside for industrial and medical use rather than for any special resonance with water. In both cases the centimetre is the natural unit because the wave is the size of a hand.

One centimetre equals 10 millimetres or 0.01 metres, and is very close to 0.3937 inches.

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.