How to use this mulch and topsoil calculator
How much mulch or topsoil to order is the bed area times the depth you want to spread. A 10 by 20 foot bed at 3 inches is 50 cubic feet, or about 1.85 cubic yards. The same math applies to both materials; pick which one you are buying and the bag size sold by your garden center.
Step-by-step instructions
- Measure the bed length and width in feet. For an irregular bed, use the rectangle that contains it and expect some extra.
- Choose mulch or topsoil and the depth in inches.
- Select the bag size if you are not ordering bulk, and add an allowance only if the ground is uneven.
Calculation formula
Important assumptions and limitations
Rectangular bed and an even depth. One cubic yard is 27 cubic feet. The bag count uses the cubic-foot size you select. Settling, moisture and how the supplier measures a yard can change the delivered amount.
For material orders, confirm package yields, stock sizes and installation instructions with the actual manufacturer or supplier. Your building department determines the applicable local code; a quantity estimator is not a structural design or permit approval.
Frequently asked questions
How many cubic yards of mulch do I need?
Multiply length by width in feet by depth in inches, then divide by 324. At 3 inches, one cubic yard covers 108 square feet. At 2 inches, it covers 162 square feet.
How many bags is that?
Divide the cubic feet by the size of the bag. Fifty cubic feet is 25 bags of 2 cubic feet, or 17 bags of 3 cubic feet after rounding up.
How deep should mulch or topsoil be?
You set the depth. About 2 to 3 inches is a common starting point for mulch on planting beds. New topsoil beds are often deeper. Check the product guidance and keep mulch off plant stems and tree trunks.
We publish formulas and assumptions so you can verify an estimate. Learn about our methodology or report an issue.