The area of any surface is the number of units of area measure the surface contains. A unit of area measure is a square unit. The main thing to remember when computing for areas is that the dimensions used must be of the same unit of measureif in inches, all units must be in inches and if in feet, all must be in feet.

Figure 1-4.-Geometric figures of a triangle, quadrilateral, pentagon, hexagon, heptagon, and octagon.

Figure 1-5.-Geometric figures of a trapezoid, trapezium, rhombus, and rhomboid.

Figure 1-6 shows a rectangle measuring 10 ft by 8 ft, divided up into units of area measure, each consisting of 1 sq ft. If you were to count the units, one after the other, you would count a total of 80 units. However, you can see that there are 8 rows of 10 units, or 10 rows of 8 units.

Therefore, the quickest way to count the units is simply to multiply 10 by 8, or 8 by 10.

You could call the 8-ft dimension the width and the 10-ft dimension the length, in which case you would say that the formula for determining the area of a rectangle is the width times the length, or A = w1. Or, you could call the 10-ft dimension the base and the 8-ft dimension the altitude (meaning height), in which case your formula for area of a rectangle would be A = bh.