How many cubic yards or bags of mulch a bed needs, at the depth that actually suppresses weeds.
Mulch Calculator
Inputs
3 in suppresses weeds. Under 2 in will not.
Bagged mulch is usually 2 ft³ in the US.
Results
Mulch needed
0.74 yd³
V = L × W × (depth ÷ 12); bags = ft³ ÷ bag size
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Mulch is a straight area-and-depth calculation with no compaction — it is not going to be rolled. What makes it worth a calculator is that it is sold two ways at once, in cubic yards for bulk and 2 cubic foot bags at retail, and the two prices are not remotely comparable per unit.
Depth matters more than most people expect. Below about 2 inches mulch does not suppress weeds, which is usually the entire reason for laying it.
V = length(ft) × width(ft) × (depth(in) ÷ 12)yd³ = ft³ ÷ 27bags = ft³ ÷ bag size (usually 2 ft³)one yd³ covers 108 ft² at 3 inOne cubic yard is 27 cubic feet. At 3 inches deep — a quarter of a foot — that spreads over 108 square feet. At 2 inches it covers 162 square feet; at 4 inches, 81. Those three numbers cover almost every landscaping order you will ever place.
Three inches blocks enough light to suppress most annual weeds while still letting water through. Two inches is marginal. Four or more starts holding moisture against stems and can encourage rot, particularly against tree trunks and shrub bases.
A cubic yard is 13.5 bags at the standard 2 cubic feet. Bagged mulch commonly runs $3–$6 a bag, so a yard in bags is $40–$80 against $30–$50 delivered in bulk — before you have carried 13 bags from the car. Bulk wins on anything above about 2 yards; bags win when you cannot get a truck to the bed.
About 0.4 tons per cubic yard, roughly 800 lb — less than a third the weight of gravel. A pickup can carry two to three yards where it would struggle with one yard of stone. Wet mulch is considerably heavier.
A single planting bed along a fence.
0.74 yd³, or 10 bags
Under a yard. Bags are reasonable here — a bulk delivery charge would exceed the material cost.
A full front garden refresh.
5.6 yd³ — order bulk
75 bags is roughly $300 and a full day of carrying. The same mulch in bulk is around $200 delivered, tipped in one pile.
A mulch ring, 6 ft across, with the trunk kept clear.
4 bags
Keep mulch a few inches clear of the trunk. Piling it against bark holds moisture there and rots the tree — the "mulch volcano" is one of the most common ways gardens kill their own trees.
| Depth | Coverage | Bags (2 ft³) |
|---|---|---|
| 1 in | 324 ft² | 13.5 |
| 2 in | 162 ft² | 13.5 |
| 3 in | 108 ft² | 13.5 |
| 4 in | 81 ft² | 13.5 |
| 6 in | 54 ft² | 13.5 |
| Purpose | Depth |
|---|---|
| Weed suppression | 3 in |
| Moisture retention | 2–3 in |
| Decorative only | 2 in |
| Playground safety surfacing | 9–12 in |
| Around tree trunks | 3 in, kept clear of bark |
| Top-up over existing mulch | 1–2 in |
| Type | Lasts | Notes |
|---|---|---|
| Shredded hardwood | 1–2 years | Most common, knits together on slopes |
| Pine bark | 2–3 years | Acidic — suits azaleas and rhododendrons |
| Cedar | 2–3 years | Naturally insect resistant |
| Straw | 4–6 months | Vegetable beds; cheap but short-lived |
| Rubber | 10+ years | Playgrounds; does not decompose or feed soil |
Mulch is a recurring cost, not a one-off. Organic mulch breaks down — that is the point of it — so most beds need a top-up every one to two years.
Typically $30–$50 per cubic yard for standard hardwood, plus $50–$100 delivery. Dyed and premium mulches run $40–$70. Some municipalities give away wood chips free if you can collect them.
$3–$6 for a 2 cubic foot bag, which is $40–$80 per cubic yard — meaningfully more than bulk. Worth it below about two yards, or when a truck cannot reach the beds.
$50–$100 per cubic yard spread, or roughly $0.50–$1.00 per square foot including material. Spreading mulch is genuinely easy work, so this is one of the more worthwhile DIY savings.
Hardwood mulch needs topping up every year or two at 1–2 inches, which is roughly a third to a half of the original volume. Worth budgeting as an annual line rather than a one-time purchase.
The "mulch volcano" holds moisture against bark, which rots it and invites pests and disease. Mulch should be a flat ring with a few inches of clear space around the trunk, not a cone.
Under 2 inches lets enough light through for weeds to come up regardless, so the money achieves nothing on the one job it was bought for. Three inches is the working figure.
Over 4 inches on a planting bed holds water against stems and can starve roots of air. Deep mulch belongs on playgrounds, not around perennials.
The crossover is around two cubic yards, or 27 bags. Above it you are paying roughly double for the privilege of carrying it yourself.
Planting beds are almost never rectangular. Curved and kidney-shaped beds measured as their bounding box over-order significantly — split them into simpler shapes and add the results.
Multiply bed area by depth in feet. At the usual 3 inches, one cubic yard covers about 108 square feet. A 20 × 4 ft border at 3 inches needs 0.74 cubic yards, or 10 bags.
13.5 bags at the standard 2 cubic feet per bag. A cubic yard is 27 cubic feet.
Three inches. Below 2 inches it lets enough light through for weeds to grow anyway; above 4 inches it holds moisture against stems and can starve roots of air.
About 800 lb, or 0.4 tons — less than a third the weight of gravel. Wet mulch is considerably heavier.
Bulk, above about two cubic yards. A yard in bags is $40–$80 against $30–$50 delivered in bulk — and 13 bags to carry. Bags win when a truck cannot reach the beds.
Hardwood mulch needs a 1–2 inch top-up every one to two years as it breaks down. That is roughly a third to a half of the original volume, so it is worth budgeting annually.
No. Piling mulch against bark — the "mulch volcano" — holds moisture there, rots the trunk and invites pests. Keep a few inches of clear space around the trunk.
A 2 cubic foot bag covers 8 square feet at 3 inches deep, or 12 square feet at 2 inches.
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