Bed size and depth in — cubic yards, bag count and cost out, including the one number every garden centre quotes you in: how many bags make a yard.
2 in around annuals and vegetables · 3 in for most shrub and perennial beds · 4 in around trees or to suppress weeds. Deeper than 4 in suffocates roots.
Densities are for damp, settled material. A wet load can weigh half again as much — matters only if you are hauling it yourself.
%
Fresh mulch settles roughly 5–10% in the first few weeks. Add a little so the bed still looks full in a month.
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You need
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Bed area—
Volume—
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Bags needed—
Approx. weight—
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The calculation
Area × depth = volume. The only trap is that depth is quoted in inches while beds are measured in feet, so the depth has to be divided by 12 first. A 10 × 25 ft bed at 3 inches is 250 ft² × 0.25 ft = 62.5 ft³, and because a cubic yard is 27 ft³, that is 2.3 cubic yards.
Bags per yard — the number garden centres never volunteer
Standard mulch bags hold 2 cubic feet, so a cubic yard is 13.5 bags. That single figure is what makes bulk delivery look expensive until you do the arithmetic: 13.5 bags at $4.50 is $60.75 a yard, against roughly $35–$45 a yard delivered.
Bag size
Bags per cubic yard
Coverage at 3 in
1 ft³
27
4 ft²
1.5 ft³
18
6 ft²
2 ft³
13.5
8 ft²
3 ft³
9
12 ft²
Depth is a horticultural decision, not just a volume one
Two inches is enough to hold moisture in a vegetable bed and lets rain through easily. Three inches is the standard for shrub and perennial beds — deep enough to block most weed germination without staying soggy. Four inches is for weed-heavy ground or around established trees. Beyond that, mulch starts to behave like a lid: water runs off it, roots grow up into it, and bark can go anaerobic and sour.
Mulch is one of the few landscaping materials where the two ways of buying it — bagged and bulk — differ enough in price that the decision is worth a minute of arithmetic. Bags are convenient, clean and easy to store; bulk is roughly a third cheaper per cubic yard but arrives as a pile on your driveway that you are then obliged to move.
The crossover is usually around three cubic yards. Below that, delivery fees dominate and bags win. Above it, bulk pulls ahead quickly, and by six or seven yards the saving is larger than the cost of hiring help to spread it.
Measure the beds, not the garden
The most common over-order comes from measuring a rectangle around a bed that is not rectangular. Curved borders typically enclose 20–30% less ground than the bounding box suggests. Break an irregular bed into two or three simple shapes, calculate each, and add them — or pace the perimeter and use the circle option for anything roughly round.
Keep it off the trunk
Whatever the depth, mulch should taper to nothing in the last few inches before a trunk or stem. Piled against bark it traps moisture, invites rot and gives voles somewhere to work unseen. The volume difference is negligible; the difference to the plant is not.
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Frequently asked questions
How many bags of mulch are in a cubic yard?
Thirteen and a half standard 2 cubic foot bags make one cubic yard, because a cubic yard is 27 cubic feet. If your bags are 1.5 ft³ it takes 18 of them, and 3 ft³ bags take 9.
How much area does one bag of mulch cover?
A 2 cubic foot bag covers about 12 square feet at 2 inches deep, 8 square feet at 3 inches, or 6 square feet at 4 inches. Coverage halves as you double the depth.
How deep should mulch be?
Three inches suits most shrub and perennial beds. Use 2 inches around vegetables and annuals, and up to 4 inches where weed pressure is heavy. Deeper than 4 inches restricts water and air reaching the roots.
How much does a yard of mulch weigh?
Between 400 and 800 pounds for wood mulch depending on type and how wet it is — around 500 lb dry for shredded bark. Compost runs closer to 1,200 lb per yard and rubber mulch to around 1,350 lb, which matters if you are hauling it in a car trunk or half ton pickup.
Is bulk mulch cheaper than bags?
Per cubic yard, almost always — typically $35 to $45 delivered against roughly $60 worth of bags. The delivery fee is what decides it. Under about three yards the fee outweighs the saving; above that bulk is clearly cheaper.