Mulch & landscaping
How Much Mulch Do I Need for Your Garden Beds?
By the HomeCalc USAReviewed against our editorial policyLast updated US units and pricing
Bed area in square feet x depth in inches, divided by 324, gives cubic yards of mulch. One cubic yard equals 13.5 standard 2 cubic foot bags and covers about 162 square feet at 2 inches deep.
Skip the arithmetic: use the Mulch & Topsoil Calculator.
Key takeaways
- 324 is the magic number: square feet x inches deep / 324 = cubic yards.
- Two to three inches is right for most beds; three to four inches around trees and shrubs, never piled against the trunk.
- Bulk mulch beats bags on price above about 3 cubic yards, roughly 40 bags.
- Organic mulch breaks down and needs a 1-inch top-up each year rather than a full replacement.
The mulch formula
Mulch is sold loose by the cubic yard or bagged in 2 cubic foot bags. Because depth is measured in inches and volume in cubic yards, the shortcut divisor is 324 (27 cubic feet per yard x 12 inches per foot).
- Measure each bed and add up the total square footage. For a circle, use 3.14 x radius x radius.
- Pick a depth in inches.
- Square feet x depth / 324 = cubic yards.
- Multiply cubic yards by 13.5 to get the number of 2 cubic foot bags.
A worked example
Two foundation beds of 20 ft x 4 ft plus a 10-foot-diameter tree ring: 160 + 78.5 = 238.5 square feet. At 3 inches, 238.5 x 3 / 324 = 2.21 cubic yards, or about 30 bags. At that size, bulk delivery is usually the cheaper option even after the delivery fee.
Coverage table
One cubic yard of mulch
| Depth | Coverage per cubic yard | Coverage per 2 cu ft bag |
|---|---|---|
| 1 in | 324 sq ft | 24 sq ft |
| 2 in | 162 sq ft | 12 sq ft |
| 3 in | 108 sq ft | 8 sq ft |
| 4 in | 81 sq ft | 6 sq ft |
How deep, and where
- Annual and perennial beds: 2 inches. More can suffocate shallow roots and hide crown rot.
- Shrub borders: 3 inches.
- Around trees: 3-4 inches spread in a wide ring, pulled back 3-6 inches from the trunk flare. Volcano mulching invites bark rot and girdling roots.
- Vegetable gardens: 1-2 inches of straw or fine compost so the soil still warms in spring.
- Slopes: shredded hardwood knits together and resists washing; nuggets float away.
Mulch types compared
| Type | Lasts | Best for |
|---|---|---|
| Shredded hardwood | 1-2 years | General beds, slopes |
| Pine bark nuggets | 2-3 years | Shrub beds, acid lovers |
| Pine straw | 1 year | Southeast landscapes, slopes |
| Cedar / cypress | 2-3 years | Formal beds, insect resistance |
| Rubber mulch | 10+ years | Playgrounds, not planting beds |
| Compost | Under 1 year | Feeding soil, vegetable gardens |
Weight, delivery and handling
Dry shredded mulch weighs roughly 400-800 pounds per cubic yard; soaked, it can approach 1,000. A half-ton pickup safely carries about 2 cubic yards of dry mulch, a full-size truck bed about 3.
Bulk mulch is normally dumped in the driveway, so plan a tarp and a wheelbarrow route. One person moves about 1 cubic yard per hour with a wheelbarrow and a mulch fork.
When to mulch
Mid to late spring, once soil has warmed, is the main application. Mulching too early keeps the ground cold and slows growth. A second light top-up in late fall protects roots from freeze-thaw heaving in cold zones.
Before adding, rake and fluff last year's layer. Old mulch that has matted can shed water instead of absorbing it, and the fresh depth measurement should include what is already there.
Frequently asked questions
What is the standard mulch bag size?
Most US bagged mulch is sold in 2 cubic foot bags; some brands sell 1.5 or 3 cubic foot bags. At 3 inches deep, a 2 cubic foot bag covers about 8 square feet. Check the bag label for its stated volume.
How many bags of mulch are in a cubic yard?
13.5 bags at the standard 2 cubic feet per bag. Three cubic foot bags work out to 9 per cubic yard.
How much does a yard of mulch cover?
162 square feet at 2 inches deep, or 108 square feet at 3 inches.
Should I remove old mulch before adding new?
Usually not. Organic mulch decomposes into the soil. Rake it loose and top up by about an inch. Remove it only if total depth already exceeds 4 inches or it has grown a matted crust.
Is bulk mulch cheaper than bags?
Above roughly 3 cubic yards it almost always is, even including delivery. Bags win for small beds and for anyone without space for a dumped pile.
Sources and references
- US Forest Service — Mulching trees correctly — Guidance on mulch depth and keeping mulch off the trunk flare.
- USDA Plant Hardiness Zone Map — Used to judge regional timing for spring and fall mulching.