How Much Mulch Do I Need?

Updated October 31, 2026

Mulch for a bed is a volume. Length and width are the footprint. Depth is how thick you want the layer. Bulk suppliers sell that volume in cubic yards, usually in quarter-yard steps. A bag is a smaller volume printed on the plastic, and it is a different purchase from a truckload.

Measure the bed you will cover

Measure length and width out to where the mulch stops, not out to a fence the bed never reaches. Feet are the convenient unit. A curved outline can be boxed as one rectangle that contains it. You will be a little long, and the extra rakes out. Coming up short means a second trip.

One rectangle is one calculation. Two beds that really are the same size can share the calculator’s “number of areas” field. Two beds that differ are two runs. Averaging the widths undercounts the larger bed.

Turn inches of depth into feet

Depth is usually read in inches. The volume formula needs feet, so divide inches by 12 before you multiply.

• 2 inches = 2 ÷ 12 of a foot.
• 3 inches = 3 ÷ 12 = 0.25 feet.
• 4 inches = 4 ÷ 12 of a foot.

Two or three inches is the usual finished depth on an open bed. Four inches piled against a trunk or a shrub crown is more than most plantings want. The arithmetic will still accept it.

A 10 by 12 foot bed at 3 inches

One bed, 10 feet by 12 feet, 3 inches deep.

• Depth in feet: 3 ÷ 12 = 0.25 ft.
• Cubic feet: 10 × 12 × 0.25 = 30 cu ft.
• Cubic yards: 30 ÷ 27 = 1.11 cu yd.

There are 27 cubic feet in a cubic yard. 1.11 cubic yards is the bed with nothing extra. It is not the number to give the yard if the edges wander or you are filling a layer that has already sunk in the middle. The same division by 27 is how a concrete slab becomes yards. The depth and the material are different. Slab measuring is covered in How Much Concrete Do I Need for a Slab?.

What one cubic yard covers

Coverage is 27 cubic feet divided by the depth in feet. It is the sanity check on the bed measurement, not a second order.

• At 2 inches: 27 ÷ (2 ÷ 12) = 162 square feet.
• At 3 inches: 27 ÷ 0.25 = 108 square feet.
• At 4 inches: 27 ÷ (4 ÷ 12) = 81 square feet.

The example bed is 10 × 12 = 120 square feet. At 3 inches, 120 is more than 108, which is why the exact volume is a bit over one yard. At 2 inches, 120 is under 162, so the exact volume is under one yard.

Add waste, then round to the next quarter yard

Waste is extra mulch so the bed can finish level. It is not a returnable leftover. The calculator accepts 0, 5, 10, 15, or 20 percent.

• 5% — one rectangle, edges you can see, and you are only refreshing a layer that is already close to the depth you want.
• 10% — the default. On the 3 inch example, 1.11 × 1.10 = 1.22 cubic yards.
• 15% — a curved outline, or several beds on one ticket.
• 20% — a first delivery where you have not checked the low spots.

After waste, the bulk order rounds up to the next 0.25 cubic yard. 1.22 cubic yards becomes 1.25. The same 10 by 12 bed at 2 inches is 20 cubic feet, 0.74 cubic yards exact, 0.81 with 10 percent waste, and the order rounds to 1.00 cubic yard. Stopping at 0.75 would put you under the volume you just calculated.

Bags are a different purchase

The calculator estimates bulk cubic yards. It does not count bags. Read the cubic feet printed on the bag in your hand.

• A 2 cubic foot bag: 27 ÷ 2 = 13.5 bags per cubic yard. 1.25 yards × 13.5 = 16.875, so 17 bags.
• A 3 cubic foot bag: 27 ÷ 3 = 9 bags per cubic yard. 1.25 yards × 9 = 11.25, so 12 bags.

If the bag states a different yield, use that yield. A yard of bags costs more than a yard of bulk and makes sense when the bed is small or a truck cannot reach it. The price field on the calculator is dollars per cubic yard of bulk. It does not price bags, a delivery fee, or tax.

What this volume leaves out

The yards above are mulch only. Fabric, edging, and plants are separate. Do not treat 1.25 cubic yards as the whole ticket until the yard tells you the minimum load. If you type a price per cubic yard, the cost line is that price times the recommended yards.