How to measure your garden beds
For a rectangular bed, measure the length and width in feet. For a ring of mulch around a tree, measure across the full circle. If your beds have curves or odd shapes, break them into rough rectangles and circles, work out the area of each one, and use I know the area to enter the total.
A quick way to measure a curved bed is to lay a garden hose around its edge, then straighten the hose and measure it. That gives you the perimeter, and you can estimate the shape from there.
How the calculation works
Area (sq ft) = length × width, or 3.1416 × (diameter ÷ 2)² for a circle
Volume (cu ft) = area × (depth in inches ÷ 12)
Cubic yards = cubic feet ÷ 27
Bags = cubic feet ÷ bag size, rounded up
In the example above, a 20 × 4 ft bed is 80 square feet. Spread 3 inches deep, that takes 20 cubic feet of mulch: 0.74 cubic yards, or 10 bags of 2 cubic feet.
How deep should mulch be?
- 2 to 3 inches is the depth most garden experts recommend for beds around shrubs and perennials. It holds moisture and keeps most weeds down.
- 1 inch is usually enough to refresh last year's mulch, since the old layer is still breaking down underneath.
- More than 4 inches can keep water and air from reaching the soil, so avoid going deeper unless you are covering a path.
Keep mulch a few inches away from tree trunks and plant stems. Piling it up against the bark, sometimes called a mulch volcano, traps moisture and can lead to rot and pests.
Bags or bulk mulch?
Bagged mulch is easy to carry and store, and it is the simpler choice for small beds. Bulk mulch, sold by the cubic yard from a landscape supplier, is usually cheaper per yard for bigger jobs, but you may pay for delivery and need a place to dump the pile. One cubic yard is the same as 13.5 bags of 2 cubic feet or 9 bags of 3 cubic feet, so you can compare prices directly.
| Depth | Area one cubic yard covers |
|---|---|
| 1 inch | 324 sq ft |
| 2 inches | 162 sq ft |
| 3 inches | 108 sq ft |
| 4 inches | 81 sq ft |
Frequently asked questions
How many bags of mulch are in a yard?
13.5 bags of 2 cubic feet, or 9 bags of 3 cubic feet. A cubic yard is 27 cubic feet.
How much area does a 2 cubic foot bag of mulch cover?
About 12 square feet at 2 inches deep, or 8 square feet at 3 inches deep.
How much mulch do I need for 100 square feet?
At 3 inches deep, 100 square feet needs 25 cubic feet of mulch. That is 0.93 cubic yards, or 13 bags of 2 cubic feet.
Does this work for stone or rubber mulch?
Yes, for the volume. Decorative stone is often sold by the ton, so use our gravel calculator to convert the volume to weight.
This calculator gives an estimate for buying materials. Mulch settles after it is spread, so the depth you measure a few weeks later may be slightly less.