Small gardens often require a relatively small amount of topsoil, so a bag or two from a gardening center typically covers the need. For large spaces, buying bulk material is often the cheapest option. Since bulk topsoil is sometimes retailed by the cubic yard, you need to measure the specific area correctly to obtain the total square footage. You will use that figure to calculate the volume, or total cubic yardage of material to purchase. One cubic yard can be expressed as 1 yard cubed or 27 cubic feet. If you ever doubted the value of high school geometry, now is the time to give it a go.
Measure the length and width of any rectangular or square gardening area with a measuring tape. Multiply the length and width figures together to obtain the area’s total square footage. An area 20 feet long and 10 feet wide has a total of 200 square feet.
Split an L-shaped gardening area into two simple rectangles with a piece of string. Measure each rectangle and calculate its square footage. Add the separate calculations together for the total square footage of the gardening area.
Calculate a 90-degree, or right, triangle’s square footage by measuring its height and base. Multiply the height by the base. Divide that number by 2 to determine the triangle’s total square footage.
Divide a triangle with a piece of string if the shape is not a right triangle. Run the string from the shape’s highest point down to a point directly underneath on its base to bisect the area into two right triangles. Calculate the square footage of each right triangle separately. Add the two figures together for total square footage of the gardening area.
Measure a round garden from any spot on its outer edge, or perimeter, to the center point of the circle to get the radius. Square this figure, or multiply it by itself. Multiply that number by 3.14, or pi, to get the square footage of the circle.
Multiply the width of an oval area by its length. Multiply that product by .08 to get the oval’s square footage.
Multiply any garden’s total square footage by the number of inches in depth of topsoil you need -- but remember to convert the inches to feet first. This gives you the area’s cubic footage, which you will use to determine cubic yardage. If your garden measures 15 feet long and 5 feet wide and you need 4 inches of topsoil, multiply the three numbers together with the depth expressed as a decimal. In this instance, the decimal form of 4 inches, converted to feet, is .333, so 15 times 5 times .333 gives you 24.975 cubic feet. Divide that by 27, which is the number of cubic feet in 1 cubic yard. This gives you 0.925, or slightly less than 1 cubic yard of topsoil.
Things You Will Need
- Measuring tape
- Caputo Recycling notes that a single cubic yard of topsoil 2 inches deep covers 162 square feet. Two cubic yards is enough to cover 324 square feet, 2 inches deep.
- Express inches as decimals, or portions of a foot, to convert cubic feet into cubic yards. The decimal form of 1 inch is 0.0833, 2 inches is 0.167, 3 inches is 0.25, 4 inches is 0.333, 5 inches is 0.417, 6 inches is 0.5, 7 inches is 0.583, 8 inches is 0.667, 9 inches is 0.75, 10 inches is 0.833, 11 inches is 0.917, and 12 inches is 1.0.
- One cubic yard of topsoil weighs between 1,700 and 2,000 pounds, depending upon the material‘s moisture level. The American Topsoil company says most half-ton pickup trucks can manage this safely. Heavier-duty one-ton and 3/4-ton pickups can often hold and handle up to 2 cubic yards, or about 4,000 pounds.
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