Short answer
A 15×6 garden bed mulched to 4 inches deep requires 1.11 cubic yards of mulch. That translates to 15 bags at 2 cubic feet each, weighs roughly 0.44 tons, and fits in a single pickup load. For cubic yards of mulch for a 15x6 medium garden bed 4 inches deep, 1.11 cubic yards is your baseline before any waste adjustment.
How this calculator works
The calculation converts three inputs — bed length, bed width, and mulch depth — into cubic yards, which is the standard unit for both bulk mulch orders and bag-count estimates.
The inputs for this variant:
- Bed length: 15 ft
- Bed width: 6 ft
- Mulch depth: 4 in
Step 1 — Bed area
Multiply length by width: 15 × 6 = 90 square feet. This is the footprint that needs to be covered. It doesn't account for plants or shrubs that displace soil; if you have large established shrubs, subtract their base area from the 90 sq ft before running the numbers.
Step 2 — Convert depth to feet
Mulch depth is entered in inches because that's how people think about it, but the volume formula needs consistent units. Dividing 4 inches by 12 gives 0.333 feet.
Step 3 — Cubic feet
Multiply area by depth in feet: 90 × 0.333 = 30 cubic feet.
Step 4 — Convert to cubic yards
Divide cubic feet by 27 (there are 27 cubic feet in one cubic yard): 30 ÷ 27 = 1.11 cubic yards.
Secondary outputs
The calculator also produces these derived numbers:
- Bag count: One cubic yard equals 13.5 bags of 2-cubic-foot mulch. Multiply 1.11 × 13.5 = 14.99, rounded up to 15 bags. The calculator always rounds up because you can't buy a partial bag.
- Weight in tons: Mulch averages about 800 lbs per cubic yard (this varies — fresh-cut wood chips are heavier; dry, aged cedar is lighter). At 800 lbs/yd³: 1.11 × 800 = 889 lbs, or 0.44 tons.
- Truckload class: Bulk mulch deliveries are typically quoted in cubic yards, and a standard delivery truck carries about 5 cubic yards. At 1.11 cubic yards, you need 1 truckload class — though this bed is small enough that a pickup haul from a landscape supply yard is more practical.
Waste factor
The default 10% waste factor accounts for uneven spreading, material that falls outside the bed edges, and the small amount left clinging to bags or the delivery pile. Applied here: 1.11 × 1.10 = 1.22 cubic yards — effectively 16 bags if you want a buffer. For a precisely edged bed where you're a careful spreader, the base 1.11 cubic yards (15 bags) is workable.
Why depth matters more than you might expect
Increasing depth from 3 inches to 4 inches on this same 90 sq ft bed adds 0.28 cubic yards — almost 4 more bags. If you're debating between 3 and 4 inches, know that 4 inches provides measurably better weed suppression and moisture retention through summer heat, but it costs roughly 33% more material. For ornamental beds with established plants, 4 inches is worth it. For a bed you're heavily amending each season anyway, 3 inches does the job.
Recommended materials
For a bed this size, bagged mulch is easier to handle than a bulk delivery — 15 bags is a one-trip load in any mid-size vehicle. Pairing the right mulch with edging and weed fabric makes the installation last.
- Vigoro cedar mulch (2 cubic ft bag) — shredded cedar resists compaction better than dyed wood chips and has natural oils that slow decomposition; plan on 15 bags for this bed
- Master Mark plastic landscape edging (20 ft x 5 in) — keeps mulch from migrating onto lawn or hardscape; one 20 ft coil handles the perimeter of this 15 ft bed
- ECOgardener premium weed barrier landscape fabric (3x50 ft) — install before mulching in ornamental beds; the 3 ft roll width lines up cleanly with a 6 ft wide bed using two side-by-side strips
FAQ
How many cubic yards of mulch does a 15x6 bed at 4 inches deep require? It requires 1.11 cubic yards. That accounts for the 90 square feet of bed area multiplied by the 4-inch depth converted to feet (0.333 ft), then divided by 27 to reach cubic yards.
How many 2-cubic-foot bags do I need for this bed? You need 15 bags. One cubic yard equals 13.5 bags of 2 cubic foot mulch, so 1.11 cubic yards rounds up to 15 bags.
Should I add a waste factor for mulch? A 10% waste factor is standard for mulch. It covers uneven spreading, low spots, and material left in the bag. For this bed, that means buying closer to 1.22 cubic yards or rounding up to 16 bags.
How deep should mulch be in a garden bed? Most beds do well with 2 to 4 inches. At 2 inches, mulch suppresses light weed growth and retains moisture. At 4 inches, it provides stronger weed suppression and better moisture retention during dry stretches, though deeper than 4 inches can suffocate plant roots.
What does 1.11 cubic yards of mulch weigh? At the standard estimate of 800 lbs per cubic yard, 1.11 cubic yards weighs roughly 889 lbs — about 0.44 tons. Actual weight varies by mulch type and moisture content.
Can I fit this in a pickup truck? Yes. One standard truckload class covers 5 cubic yards, and 1.11 cubic yards fits comfortably in a half-ton pickup bed. A standard short bed holds roughly 1 to 1.5 cubic yards of loose mulch without overflow.
Does mulch type change the volume needed? No — volume is determined by the bed dimensions, not the mulch type. Type affects weight, longevity, and price per yard. Shredded cedar lasts longer than dyed wood chips; pine bark nuggets settle less than fine-ground material.
Do I need landscape fabric under mulch? It depends on the bed. Weed barrier fabric under mulch meaningfully reduces weed pressure in ornamental beds. Skip it in vegetable gardens — the fabric blocks the organic matter from decomposing into the soil.
How do I convert square feet to cubic yards manually? Multiply length × width to get square feet, then multiply by depth in inches divided by 12 to get cubic feet, then divide by 27 to get cubic yards. For this bed: 15 × 6 × (4/12) / 27 = 1.11 cubic yards.
How often should I replenish mulch? Most organic mulches break down within one to two years. Check depth each spring — if it has compacted to under 2 inches, top it off. You typically need to add 1 to 2 inches per year rather than replacing the full depth.
What is the difference between a cubic yard and a cubic foot of mulch? One cubic yard equals 27 cubic feet. Bulk mulch is sold by the cubic yard; bagged mulch typically comes in 2-cubic-foot bags, so one cubic yard equals 13.5 of those bags.