Crushed stone can beautify your landscaping and help reduce weeds. Walkways should have at least a 2-inch depth of stone, set on top of 2 inches of packed sand. Other areas may require anywhere from 1 to 6 inches of stone depth, depending on how much erosion you expect and the area's purpose. Use thinner layers of 1 to 2 inches for a groundcover around plants and stones, crushed to 1/2 inch or smaller. Choose thicker depths for rock gardens or larger pieces of crushed stone.
Measure the length and width, in feet, of the area you want to cover with stone. For circular areas, measure the diameter. For irregular shapes, measure the length and width at the widest point; this will leave you with some extra stone. Round your measurement off to the nearest 3 inches, which equals 0.25 feet. For example, for a 4-foot, 2-inch-long garden, round up to 4.25 feet.
Multiply the length and width of your area together for rectangular or irregular shapes. Divide the diameter of a circular area in half to get the radius, and then multiply that radius by itself and multiply that result by 3.14, also called "pi." These formulas will give you the area in square feet. For example, a 4-foot 2-inch by 6-foot 6-inch garden would be 4.25 feet times 6.5 feet, or 27.625 square feet.
Divide the number of inches deep you want your stone by 12 to get an answer in feet. For example, 2 inches is 0.1666666 (repeating). Round to the second decimal place for an easily manageable answer: in this case, 0.17 feet.
Multiply your square foot result by the depth result. In this case, that is 27.625 times 0.17, which results in 4.69625 cubic feet. Crushed stone is generally sold in cubic feet, so in this case you would need 5 cubic feet.
Check with the manufacturer for the approximate weight per cubic foot of the stone you want if it is sold by weight rather than volume. Multiply the weight per cubic foot by the number of cubic feet you need to determine how many pounds to buy.