Calculate cubic yards, cubic feet, and number of bags of mulch needed for your garden or landscaping beds.
| Purpose | Recommended Depth |
|---|---|
| Weed suppression | 3–4 inches |
| Moisture retention | 2–3 inches |
| Annual beds | 2–3 inches |
| Perennial beds | 3–4 inches |
| Tree / shrub rings | 3–4 inches |
| Vegetable garden | 2–3 inches |
| Slopes / erosion control | 4–6 inches |
| Playground safety | 6–12 inches |
| Bag Size | @ 2" deep | @ 3" deep | @ 4" deep |
|---|---|---|---|
| 1 cu ft | 6 ft² | 4 ft² | 3 ft² |
| 2 cu ft | 12 ft² | 8 ft² | 6 ft² |
| 3 cu ft | 18 ft² | 12 ft² | 9 ft² |
Since an international agreement in 1959 fixed the yard at exactly 0.9144 metres, the cubic yard that bulk mulch is sold by has had one exact size: 0.764554857984 cubic metres, or 27 cubic feet. That conversion is the last step of this calculator. It turns a bed's length, width and depth into cubic feet, cubic yards, a rounded-up bag count and an approximate weight.
Area (sq ft) = length × width. Volume (cu ft) = area × depth in inches ÷ 12. Cubic yards = cubic feet ÷ 27. Bags = cubic feet ÷ bag size, rounded up. Weight = cubic feet × the density for the material you pick.
What changes if depth changes? A 20 × 8 ft bed (160 sq ft) needs 26.67 cu ft at 2 inches (0.99 cubic yards, 14 bags), 40 cu ft at 3 inches (20 bags), 53.33 cu ft at 4 inches (27 bags) and 80 cu ft at 6 inches (40 bags). Volume scales directly with depth, so one extra inch on this bed costs six or seven more bags. Switching bag size alters only the count: the same 40 cu ft is 40 bags of 1 cu ft or 14 bags of 3 cu ft. The material choice only changes weight, from 320 lb for straw to 1,760 lb for rubber at that volume. And if you type 3 with the unit still set to feet, the page reads three feet and returns 480 cu ft, 17.78 cubic yards and 240 bags.
Worked example: 20 ft by 8 ft, 3 inches deep, shredded bark at 20 lb per cu ft, 2 cu ft bags. Area is 160 sq ft. Volume is 160 × 3 ÷ 12 = 40 cu ft. Cubic yards are 40 ÷ 27 = 1.48. Bags are 40 ÷ 2 = 20. Weight is 40 × 20 = 800 lb. The yard figure is shown to two decimals and the bag count is always rounded up.
27 cubic feet divided by the bag size: 13.5 bags of 2 cu ft, 9 bags of 3 cu ft, or 27 bags of 1 cu ft. Bulk delivery is often cheaper per cubic foot on bigger jobs, but it needs a place to drop it.
The depth guide on the page suggests 2 to 3 inches for annual beds and vegetables, and 3 to 4 inches for perennials, shrubs and tree rings. Keep mulch off the trunk or stems instead of piling it against them.
Use area = π × radius² and enter an equivalent length and width. A 6-foot circle is about 28.3 sq ft; at 3 inches deep that is 7.07 cu ft, so 4 bags of 2 cu ft.
It is approximate. The densities are rough averages, and wet mulch weighs noticeably more than dry. Use the figure to judge whether your trailer or car can carry it, not for a delivery manifest.
Mulch settles and breaks down, and edges are never perfectly level. Rounding up to the next whole bag is built in; for bulk orders, many people add a small margin to the cubic-yard figure.