Use the classical definition of a square meter of area, equal to the portion of the plane bounded by the sides of the square long, one meter. This follows from the mathematical determination of the area of a rectangle a special case of which is square, as the works of its length and width.
Use the appropriate multiplier if you want to define square meter using the derived unit of area. For example, to determine it through square centimeters, so multiplier is 10000. It follows from the definition of meter given in the first step: so as to find the area need to build in the second degree the length of a side of a square, a side of one meter contains one hundred centimeters, the multiplier will be 100∗100=10000. Similar calculations will lead to a factor of one million, if you define a square meter in terms of square millimeters. In the case of determining square meters to square kilometers using a multiplier is a number less than unity is one hundred-thousandth of a share units (0,000001).
Use the documents registered in Bureau of technical inventory or other official state or municipal authority, if it is necessary to determine the square footage of the area of the building, room or land.
Measure the length and width of the plot or premises, if need to determine how many square feet it contains. The resulting measurement values should simply be multiplied. If the configuration of the surface you want to measure in square metres, has an irregular shape, it can be divided into several sections more correct forms, determine the square of each of the areas and sum them.