Conversion from Acres to Square nautical miles

Information about the Acre (ac)

The acre is a unit of area equal to 4046.86 square metres, or 43,560 square feet. Its symbol is ac. It is the principal land measure of the English-speaking world, and unlike most imperial units it survives not as a nostalgic remnant but as a legally operative measure in the United States, Britain, Ireland, India and much of the former British empire.

Its shape explains its odd size. The acre was defined as one chain by one furlong: a strip 22 yards wide and 220 yards long, which is the area a team of oxen was reckoned to plough in a day. Ploughing with oxen favoured long narrow strips because turning the team was slow, so the unit encodes a working method rather than a geometric idea, and that is why it is not a square number of anything.

The chain that fixes its width had a second life in surveying. Gunter's chain of 22 yards divides a mile into eighty parts and an acre into ten square chains, which made land arithmetic tractable before decimal calculation. American public land was surveyed on this basis, so a section is one square mile and contains exactly 640 acres, a quarter section 160, and those numbers still shape property boundaries across the western United States.

In practice the acre is used wherever land changes hands. Farms, building plots, forestry blocks and conservation holdings in the United States and Britain are advertised in acres, agricultural yields are quoted in bushels or tonnes per acre, and pesticide and fertiliser application rates are printed per acre on the label. In India and Pakistan the acre coexists with local units, and a Punjabi killa is an acre by another name.

A useful mental picture is that an acre is a little smaller than an association football pitch, which runs to about 1.76 acres. A city block in a gridded American town is often between two and five acres. A hectare, the metric competitor, is about two and a half acres, so converting between the two never gives a round number in either direction.

There is no single legal acre worldwide. The international acre, based on the international yard of exactly 0.9144 metres, is used almost everywhere; the United States survey acre, retired at the end of 2022, was larger by about two parts in a million, which matters only when re-tracing old survey lines across long distances.

One acre equals 4046.86 square metres, 43,560 square feet, 4840 square yards, or about 0.4047 hectares.

Information about the Square nautical mile (sq nmi)

The square nautical mile is a unit of area equal to 3,429,904 square metres, or about 3.43 square kilometres. Its symbol is sq nmi. It is the area of a square one nautical mile on a side, the nautical mile being defined as exactly 1852 metres. It is the working unit of everything that happens at sea and is measured across a surface rather than along a line.

Its usefulness comes from the definition of the nautical mile itself. One nautical mile is very nearly one minute of latitude, so a square nautical mile is close to a one-minute cell on a chart. That makes it the natural grid square for anything plotted on a nautical chart, because the unit and the graticule agree without any conversion, and a navigator can read distance and area off the same scale.

Maritime law is written in nautical miles and therefore accounted in square ones. Under the international law of the sea, a coastal state has a territorial sea of twelve nautical miles, a contiguous zone of twenty-four and an exclusive economic zone reaching two hundred. The resulting areas are vast: a state with scattered island possessions can control several million square kilometres of ocean, and comparisons between such claims are usually made after converting these figures to metric.

Search and rescue planning depends on the unit directly. A search area is defined in square nautical miles, and the time to cover it follows from the search vessel's speed in knots and the sweep width of its sensors, both of which are already in nautical units. Keeping the whole calculation in one system is what allows a coordinator to estimate coverage without stopping to convert anything.

Fisheries science and naval operations use it the same way. Fish stock density is reported per square nautical mile, survey transects are spaced in nautical miles, exercise and restricted areas are drawn as blocks of them, and aviation control zones over water are described in the same terms because aircraft also navigate in knots.

For conversion, one square nautical mile is 3.43 square kilometres, 1.32 square statute miles, or about 848 acres. The ratio to the statute mile is not intuitive, since the nautical mile is only about 15 per cent longer but the square is a third larger, which is the usual consequence of squaring a length ratio.

One square nautical mile equals 3,429,904 square metres, about 3.43 square kilometres, about 1.32 square miles, or about 848 acres.