Most beds need a layer of mulch 2 to 3 inches deep. Multiply the area by the depth, divide by 27, and add about 10 percent.
Measure the bed
Find the area of each bed in square feet. For a rectangle, multiply length by width. For curved beds, break them into rectangles and circles, or measure the longest length and the average width.
Choose a depth
Two to 3 inches suits most beds. Use 3 to 4 inches for bare, weedy areas. Use 1 to 2 inches when you are only refreshing last year layer. More than 4 inches can hold too much moisture and smother roots.
Do the math
For a 10 by 20 foot bed at 3 inches: 200 square feet times 0.25 feet is 50 cubic feet, which is 1.85 cubic yards. With 10 percent extra, order about 2 cubic yards, or 27 bags of 2 cubic feet each.
Coverage per cubic yard
One cubic yard covers about 324 square feet at 1 inch, 162 at 2 inches, 108 at 3 inches, and 81 at 4 inches.
Frequently asked questions
How deep should mulch be?
Commonly 2 to 3 inches around plants, and thinner around young stems.
How much does a cubic yard of mulch cover?
About 108 square feet at 3 inches deep.
Should I remove old mulch first?
Only if it is matted or more than 3 inches deep. Otherwise, rake it and add a thin layer.