Square measure is the system used in the measurement of surfaces. The unit for the area of a surface is the square. Hence square is the name of the system used in measuring surfaces. We can describe a tabletop as being 12 inches long and 10 inches wide, or 12 by 10 inches. But these figures represent only lines, which have just one dimension–length.
A plane surface has two dimensions. In the above example, they are length and width. These dimensions can be combined into a single expression using units of square measure. Thus we describe the area of the same tabletop as 120 square inches.
Square measure of any square or rectangular plane surface is obtained by multiplying length by width. The reason for this is easily seen if we draw a picture of the tabletop and mark off its inches. A line should be drawn at every inch along the length and at every inch along the width. The two sets of lines will cross each other. This will give us 120 little squares, each measuring one inch in length and one inch in width. The measure of each is a square inch. The square measure of other geometrical figures, such as triangles and circles, can be found in a similar way by using special formulas for finding their areas. The units of square measure that describe the area of a figure depend upon the dimensional units that are used. For example, if the above table were 12 meters long and 10 meters wide, its area would be 120 square meters.
