Draw your site as accurately as possible using graph paper if available. For oddly-shaped beds, divide the area into combinations of rectangles, triangles, and/or circles. Use the following formulas to determine area:
Rectangle: Area = length x width
Circle: Area = 3.1416 x the square of the radius
Triangle: Area = 1/2 x length of base x length of height
To determine topsoil requirements for areas of varying grade, use a transit to indicate exact fill requirements...or estimate an average fill depth.