Acre - The acre is a unit of area in a number of different systems, including the imperial and U.S. customary systems. The most commonly used acres today are the international acre and, in the United States, the survey acre. One international acre is equal to 4,046.8564224 m2. One U.S. survey acre is equal to 62,726,400,000/15,499,969 m2 = 4,046.8726098 m2. One acre comprises 4,840 square yards or 43,560 square feet (which can be easily remembered as 44,000 square feet, less 1%). Because of alternative definitions of a yard or a foot, the exact size of an acre also varies slightly. Originally, an acre was a selion of land one furlong (660 ft) long and one chain (66 ft) wide; the measure appears to have begun as an approximation of the amount of land an ox could plow in one day. However, an acre is a measure of area, and has no particular width, length or shape. The acre is often used to express areas of land. In the metric system, the hectare is commonly used for the same purpose. An acre is approximately 40% of a hectare. One acre is 90.75 yards of a 53.33-yard-wide American football field. The full field, including the end zones, covers approximately 1.32 acres.
The word "acre" is derived from Old English acer (originally meaning "open field", cognate to west coast Norwegian language "ekre" and Swedish "aker", German Acker, Latin ager and Greek agros. The acre was approximately the amount of land tillable by one man behind an ox in one day. This explains one definition as the area of a rectangle with sides of length one chain and one furlong. A long narrow strip of land is more efficient to plough than a square plot, since the plough does not have to be turned so often. The word "furlong" itself derives from the fact that it is one furrow long.
Before the enactment of the metric system, many countries in Europe used their own official acres. These were differently sized in different countries, for instance, the historical French acre was 4,221 square metres, whereas in Germany as many variants of "acre" existed as there were German states. Historically, the size of farms and landed estates in the United Kingdom was usually expressed in acres (or acres, roods, and perches), even if the number of acres was so large that it might conveniently have been expressed in square miles. For example, a certain landowner might have been said to own 32,000 acres of land, not 50 square miles of land.
Hectare - Historically, the size of farms and landed estates in the United Kingdom was usually expressed in acres (or acres, roods, and perches), even if the number of acres was so large that it might conveniently have been expressed in square miles. For example, a certain landowner might have been said to own 32,000 acres of land, not 50 square miles of land.
Square Meter - The square metre (also spelled square meter, see spelling differences) is the SI derived unit of area, with symbol m2(33A1 in Unicode). It is defined as the area of a square whose sides measure exactly one metre. The square metre is derived from the SI base unit of the metre, which in turn is defined as the length of the path travelled by light in absolute vacuum during a time interval of 1/299,792,458 of a second.
Adding SI prefixes creates multiples and submultiples; however, as the unit is squared, the order of magnitude difference between units doubles from their comparable linear units. For example, a kilometre is one thousand times the length of a metre, but a square kilometre is one million times the area of a square metre. Square metres are not necessarily the same as meters squared: an area 2 metres wide by 5 metres long would be 10 square metres, while 10 metres squared means an area of 10 metres by 10 metres. So 10 metres squared equals 100 square meters.