Mulch, Topsoil & River Rock Calculator
Figure mulch, topsoil, river rock or pine straw for rectangular beds, round beds and tree rings. See bulk yards, bag counts and tons side by side.
How it's calculated
The calculator finds the bed area, multiplies by the depth in feet, and divides by 27 for cubic yards. Bags are figured by their stated volume: mulch commonly comes in 2 or 3 ft³ bags, topsoil in 0.75 or 1 ft³.
River rock is sold by weight, so yards are converted to tons at about 1.35 tons per yard. Pine straw is figured by coverage, about 50 sq ft per bale at a typical thickness.
Worked example
A 30 × 4 ft bed with 3" of mulch is 120 sq ft × 0.25 ft = 30 ft³, or 1.11 yd³. That is 15 bags of 2 ft³ mulch, or a 1½-yard bulk load.
Field notes
- Two to three inches of mulch is plenty. Deeper mulch can suffocate roots.
- Keep mulch and rock pulled back from trunks and from siding to discourage rot and insects.
- River rock 1–3" in size goes down 2–3" deep, about twice the stone diameter.
- Bulk mulch is usually cheaper than bags above about 2 yards, even with a delivery fee.
Common questions
- How many bags of mulch are in a yard?
- A cubic yard is 27 ft³, so it takes 13½ two-cubic-foot bags or 9 three-cubic-foot bags.
- How much area does a yard of mulch cover?
- At 3" deep, one yard covers about 108 sq ft. At 2" deep, about 162 sq ft.
- How much does river rock weigh?
- About 1.35 tons (2,700 lb) per cubic yard. One ton covers roughly 100 sq ft at 2" deep.
- How much area does a bale of pine straw cover?
- Roughly 40–75 sq ft depending on bale size and how thick you spread it. 50 sq ft is a good planning number.