Mulch calculator
Cubic yards and bag counts for garden beds — at the depth that actually suppresses weeds.
Calculator
Detailed breakdown
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How to use this calculator
Measure
Measure your beds in feet. For irregular shapes, break them into rectangles and add the results.
Calculate
Once you hit calculate, results update as you type. Change any number to compare options instantly.
Order
Print the estimate and take it to your supplier. Quantities are rounded up so you don't come up short.
Depth, bags versus bulk, and the mulch volcano
Mulch volume is length times width times depth, divided by 27 for cubic yards. A 20 by 10 foot bed at 3 inches deep needs about 1.85 cubic yards, or 25 of the standard 2 cubic foot bags.
Depth is the decision that matters. Two to three inches is the sweet spot: enough to suppress weeds and hold moisture, not so much that water and air stop reaching the roots. Under two inches, weeds push through. Over four, you risk suffocating shallow-rooted plants and creating a hydrophobic crust that sheds rain instead of absorbing it.
The bags-versus-bulk line sits around two cubic yards, or roughly 27 bags. Below that, bags are easier to move and store. Above it, bulk delivery is dramatically cheaper per yard — though you need somewhere to dump it and a free weekend.
One thing worth saying plainly: do not pile mulch against tree trunks. The volcano-shaped mounds you see everywhere trap moisture against the bark, invite rot and pests, and slowly kill the tree. Pull mulch back a few inches from any trunk and keep the root flare visible.
Frequently asked questions
How many bags of mulch in a cubic yard?
Thirteen and a half 2-cubic-foot bags, or nine 3-cubic-foot bags. Most retailers sell the 2 cubic foot size.
How deep should mulch be?
Two to three inches. Less lets weeds through; more can suffocate roots and shed water instead of absorbing it.
How much area does a yard of mulch cover?
At 3 inches deep, about 108 square feet. At 2 inches, roughly 162 square feet.
Bags or bulk?
Bulk is much cheaper above about two cubic yards, which is roughly 27 bags. Below that, bags are easier to handle and store.
When should I mulch?
Late spring once the soil has warmed, and again in fall in colder climates. Refresh it rather than piling more on top — total depth should stay in the two to three inch range.
Sources
Formulas and material assumptions on this page follow published industry guidance: