Mulch and Gravel Calculator
Convert a bed area and depth into cubic yards, bags and approximate tons of mulch, gravel, sand or topsoil.
Draft — figures checked, awaiting an editorial read. Not indexed.
Formula: Volume (ft³) = length × width × (depth ÷ 12). Cubic yards = ft³ ÷ 27. Tons = yards × material density.
What this calculates
This converts a bed or driveway area and a target depth into the units bulk material is sold in: cubic yards for a delivery, bags for a trip to the shop, and approximate tons since some suppliers price stone by weight rather than volume. The bag-versus-bulk crossover is the practical question it answers. A cubic yard is 13.5 standard two-cubic-foot mulch bags, and bagged material typically costs two to three times as much per unit volume — so once you are past about half a yard, a delivery is usually both cheaper and much less work.
How it works
Volume is length times width times depth, with depth converted from inches to feet by dividing by twelve. That yields cubic feet, which divides by twenty-seven for cubic yards. Bags are the cubic feet divided by the bag size, rounded up. Weight uses an approximate density per cubic yard for each material: bark mulch is light at around half a ton per yard, topsoil about 1.1, sand about 1.35, and gravel around 1.4. Those figures move with moisture content, so the tonnage is genuinely an estimate rather than a specification.
Worked example
A 20 by 10 foot planting bed with 3 inches of mulch. Volume is 20 × 10 × (3 ÷ 12) = 50 cubic feet. Divided by 27 that is 1.85 cubic yards. In two-cubic-foot bags that is 25 bags — which is a car full, twice — against under two yards delivered. At roughly 0.5 tons per yard, the delivery weighs about 0.93 tons.
Common mistakes
Entering depth in feet when the field wants inches, which produces a number twelve times too big. Second, mulching too deep: more than three or four inches holds moisture against stems and can suffocate roots, so deeper is not better. Third, ordering gravel by volume when the supplier sells by weight, or vice versa — always confirm which unit the price is quoted in, because the two differ by a factor that depends entirely on the material.
Common questions
- How many bags of mulch are in a cubic yard?
- 13.5 bags at the standard 2 cubic feet per bag, since a cubic yard is 27 cubic feet. Nine bags if they are 3 cubic feet.
- How deep should mulch be?
- Two to three inches for most beds. That is enough to suppress weeds and hold moisture without smothering roots. Keep it pulled back from tree trunks and plant stems.