Break an odd shape into simple pieces, find each area, and add them up. Then multiply by the average depth.
Split into simple shapes
Most yards are a mix of rectangles, triangles, and circles. Sketch the area on paper, draw lines that divide it into simple shapes, and measure each one. Label each piece.
Add the areas
Rectangle: length times width. Triangle: half of base times height. Circle: 3.1416 times radius squared. Add the pieces to get a total area in square feet.
Use an average depth
If the depth varies, measure it at several points and average the readings. For a steady slope, add the two end depths and divide by two.
Use the irregular area calculator
Enter the total area and the average depth, and the calculator gives cubic yards. You can type the area in square feet, square yards, square meters, or acres.
Other methods
A trundle wheel, a garden hose laid out along the edge, or a map tool with an area function all help. Add a few inches around the edge to allow for slope and spillage.
Frequently asked questions
How do I find the area of a curved bed?
Treat it as a shape between a circle and a rectangle, or break it into pieces and add them.
What if the ground is uneven?
Measure the depth in several places and use the average.
How accurate does it need to be?
Within about 10 percent is fine for most landscaping, and the waste factor covers the rest.