Area is a physical quantity expressing the size of a part of a surface. The termSurface area is the summation of the areas of the exposed sides of an object.
Units
Units for measuring surface area include:
square metre = SI derived unit
are = 100 square metres
hectare = 10,000 square metres
square kilometre = 1,000,000 square metres
square megametre = 1012 square metres
square yard = 9 square feet = 0.83612736 square metres
square perch = 30.25 square yards = 25.2928526 square metres
acre = 160 square perches or 43,560 square feet = 4046.8564224 square metres
square mile = 640 acres = 2.5899881103 square kilometres
Useful formulae
}s^2,!|s is the length of one side of the hexagon.|-|Regular octagon|2(1+sqrt)s^2,!|s is the length of one side of the octagon.|-|Any regular polygon|fraca p ,!|a is the apothem, or the radius of an inscribed circle in the polygon, and p is the perimeter of the polygon.|-|Any regular polygon|frac ,!|P is the Perimeter and n is the number of sides.|-|Any
Source:
http://en.wikipedia.org/wiki/Area