Start at one corner of the longest side of the shape, and measure to the next corner of the longest side. For a square, all four sides are equal in length, so any side can be measured.
Write this measurement as the base (B) or length (L) of the shape. Include the unit of measurement, such as inches, centimeters or feet, in all measurements.
Start at one corner of one of the base, and measure the side of the shape that is at a right angle (90º) to it. Write this measurement as the height (H) or width (W).
Calculate the perimeter (distance around the shape) by adding the measurements of each of the four sides by using the formula, perimeter = base + base + height + height. For example, using a rectangle with a base of 10 inches and a height of 5 inches, the perimeter is P = 10 + 5 + 10 + 5 = 30 inches, or 2 feet, 6 inches.
Calculate the area of the shape using the formula, area = base x height. Using the rectangle with a base of 10 inches and a height of 5 inches, the area is A = 10 x 5 = 50 inches, or 4 feet, 2 inches.
Measure and record each side of the shape. Include the unit of measurement.
Calculate the perimeter by adding the measurements of all the sides. Perimeter of a parallelogram or trapezoid = base + base + eight + height. Triangles have only three sides, so the perimeter of a triangle = base + side + side.
Divide the shape into two triangles, unless the shape already is a triangle. The area of parallelograms and trapezoids is most easily calculated using the formula for a triangle, eliminating the need to memorize multiple formulas. Draw a straight line between two opposite corners.
Measure the base of the triangle(s), usually the longest side. Measure the height of the triangle(s) from the center of the base to the tip of the triangle.
Calculate the area of the triangle(s), using the formula, area = 1/2 base x height. For a triangle with a base of 5 inches and a height of 3 inches, the area = 1/2 x 5 x 3 = 7½ inches. For parallelograms, rhombi and trapezoids, add the area of both triangles in the shape to obtain the area.
Find the center of the circle using the compass, and draw a small dot. Draw a straight line from the dot to any point on the outline of the circle. This is the radius of the circle.
Measure the length of the radius. Include the unit of measurement.
Calculate the diameter of the circle using the formula, diameter (D) = 2 x radius. For a circle with a radius of 5 inches, D = 2 x 5 = 10 inches.
Calculate the circumference (C) -- or the distance around the outline of the circle -- using the formula, C = Pi x diameter, C = 3.14 x 10 = 31.4 inches. (Pi is rounded to 3.14 in most situations).
Calculate the area of the circle using the formula, area = Pi x radius². Therefore, A = 3.14 x 5²= 78.5 inches².