Mulch calculator
Enter the size of a bed and how deep you want the mulch to see how many cubic yards it takes, and how many bags if you know the bag size.
At 3 inches deep, one cubic yard covers 108 square feet.
How it works
The calculator multiplies the area of the bed by the depth, with the depth in inches divided by 12, to get cubic feet. It divides by 27 for cubic yards. A rectangle is its length times its width. A round bed is pi times its radius squared, from the diameter you measure.
If you type the size printed on the bag, in cubic feet, it also counts bags and rounds up to a whole bag.
What one cubic yard covers
A cubic yard covers 324 square feet at 1 inch deep, 162 at 2 inches, 108 at 3 inches and 81 at 4 inches. The calculator shows the figure for the depth you enter.
How deep to spread it
Iowa State University Extension says that a layer of 3 to 4 inches of wood chips or shredded bark suits well-drained sites around trees and shrubs. On heavy soil it says 2 to 3 inches is enough, because mulch that is too deep can waterlog it. It also says not to pile mulch against the trunk of a tree.
A worked example
A bed 25 feet long and 20 feet wide is 500 square feet. At 3 inches deep it takes 500 times a quarter of a foot, which is 125 cubic feet, or 4.63 cubic yards.
With bags of 2 cubic feet, 125 divided by 2 is 62.5, so you buy 63 bags.
Sources
- Iowa State University Extension: how deep the mulch layer should be, read on 2026-10-31.
Questions
How many bags of mulch make a cubic yard?
A cubic yard is 27 cubic feet. At 2 cubic feet a bag that is 13.5 bags, so plan on 14. Use the size printed on your bag.
How deep should mulch be?
Iowa State University Extension says 3 to 4 inches of wood chips or shredded bark suits well-drained sites around trees and shrubs, and 2 to 3 inches suits heavy soil.
How do I measure a round bed?
Measure across its widest point for the diameter and choose the circle shape. The calculator takes pi times the radius squared as the area.
Can I use it for gravel or soil?
The arithmetic is the same, area times depth. The gravel, sand and soil calculator also gives tons when you know what a cubic yard weighs.
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