How Much Mulch Do I Need? A Simple Bed-by-Bed Estimating Guide
Updated 2026-07-25 · Yardly
Mulch is one of the highest-leverage things you can do in a landscape: a two- or three-inch layer suppresses weeds, holds soil moisture, and makes beds look finished. The trick is buying the right amount — too little and you’re raking a thin, patchy layer; too much and you’re paying to haul extra bags to the curb.
The mulch formula
Mulch is sold by the cubic yard, but beds are measured in feet. Convert with the same volume math every Yardly calculator uses:
(Length × Width × Depth ÷ 12) ÷ 27 = cubic yards
Depth goes in inches, because there are 12 inches in a foot. A 20-foot by 4-foot bed at 3 inches deep is 80 square feet × 0.25 foot = 20 cubic feet, divided by 27 = about 0.74 cubic yards.
The 108 rule (a quick sanity check)
One cubic yard of mulch is 27 cubic feet. Spread it 3 inches (0.25 foot) deep and it covers 27 ÷ 0.25 = 108 square feet. At 2 inches it covers 162 square feet. If your estimate surprises you, check it against that rule.
Common mistakes
- Volcano mulching. Piling mulch against a trunk traps moisture and invites rot. Keep a few inches clear around the base.
- Guessing depth. A tape measure on one bed beats an eyeball across five.
- Forgetting irregular shapes. Break L-shaped beds into rectangles, estimate each, and add them up.
Bagged vs bulk
A yard of bagged mulch is a lot of trips. As a rule of thumb, once you’re over about one cubic yard, bulk delivery is cheaper per cubic foot and saves your back. Use bags for small refresh jobs and tight access.
When in doubt, estimate a little high — a thin leftover layer is easier to fix than a mid-bed run to the store.
Frequently asked questions
How many square feet does one cubic yard of mulch cover?
At a 3-inch depth, one cubic yard covers about 108 square feet. At 2 inches it covers roughly 162 square feet. Our mulch calculator applies your exact depth.
What mulch depth is best for weed control?
A 2–3 inch layer suppresses weeds and holds moisture. Keep it a few inches away from tree trunks to avoid rot and pests.
Should I buy bagged or bulk mulch?
For beds under about one cubic yard, bags are convenient. For larger areas, bulk delivery by the yard is usually far cheaper per cubic foot.
References: QUIKRETE (concrete estimator), Portland Cement Association (placement guidance). Yardly estimates are for planning only.