Most mulch math goes wrong before the multiplication starts — at the depth. Spread fine compost 4 inches deep and you suffocate roots; spread bark nuggets 2 inches thin and weeds push straight through. This calculator fixes that first: pick your mulch type and the extension-recommended depth fills in automatically — 2 inches for fine materials like compost, 3 for shredded hardwood, up to 4 for coarse chips and straw. Then it converts your bed dimensions into cubic yards and bags, with a 10% buffer for settling.
It also answers the question the bag display at the garden center never does: when does bulk delivery beat bagged mulch? Once your project crosses about 2 cubic yards — roughly 27 standard bags — mulch by the yard usually costs less and saves you a dozen trips from the trunk. The calculator flags that point and shows your bagged total as a per-yard price so you can compare quotes like a landscaper. Enter your bed, pick your mulch, and you’ll know exactly what to order before you leave the house.
Frequently Asked Questions
How much does 1 cubic yard of mulch cover?
One cubic yard is 27 cubic feet and covers 324 square feet at 1 inch deep, 162 square feet at 2 inches, 108 square feet at 3 inches, or 81 square feet at 4 inches. A standard 2-cubic-foot bag is 1/13.5 of a cubic yard — so one yard equals about 13.5 bags.
How deep should mulch be?
It depends on the material. Fine mulches like compost, leaf mold, and double-shredded bark pack tightly and should stay at about 2 inches. Medium-texture shredded hardwood works at 3 inches. Coarse materials like wood chips and bark nuggets need 3–4 inches to suppress weeds. Going deeper than 4 inches holds excess moisture, encourages roots to grow up into the mulch layer, and can suffocate shallow-rooted shrubs.
Is bulk mulch cheaper than bagged mulch?
Usually yes, once you need about 2 cubic yards or more. Bagged mulch typically costs 2–3 times more per cubic foot than the same material delivered in bulk. Below roughly 1 cubic yard, bags win on convenience and you avoid a delivery fee. Between 1 and 2 yards, compare your local delivery fee against the bag premium — this calculator shows your bagged total as a per-yard price to make that comparison easy.
Why should mulch be kept away from tree trunks and plant stems?
Mulch piled against bark — the classic “mulch volcano” — traps moisture against the trunk, which softens bark, invites fungal rot and boring insects, and gives voles winter cover to chew the cambium. Keep mulch 2–3 inches back from stems and 6 inches back from tree trunks, and never mound it up the trunk.
How many bags of mulch do I need for 100 square feet?
At a 3-inch depth, 100 square feet needs 25 cubic feet of mulch — that is 13 standard 2-cubic-foot bags (12.5 rounded up), or about 0.9 cubic yards. At 2 inches deep, you need 17 cubic feet, which is 9 bags.