Mulch Calculator: Cubic Yards and Bags for Your Garden Beds

Mulch volume is area times depth, all in the same unit. Depth is usually given in inches, so divide by 12 to get feet; then remember that 27 cubic feet make one cubic yard — the unit bulk mulch is sold in. The shortcut professionals use: cubic yards = (length × width × depth in inches) ÷ 324.

Stone and gravel beds use exactly the same volume math — a gravel calculator applies it to driveways, paths and drainage areas.

A garden bed measures 20 ft by 10 ft, and you want 3 inches of mulch:

1. Area: 20 × 10 = 200 sq ft.
2. Depth in feet: 3 ÷ 12 = 0.25 ft.
3. Cubic feet: 200 × 0.25 = 50 cu ft.
4. Cubic yards: 50 ÷ 27 = 1.85 cu yd → round up and order 2 cubic yards.
5. Bags: 50 ÷ 2 = 25 bags of 2 cu ft mulch, or 50 ÷ 3 = 16.67 → 17 bags of 3 cu ft mulch.

Enter the same numbers above and the calculator returns every one of these figures.

Measure once, buy once.

Step by step

1. Measure the bed's length and width in feet. For curved beds, measure the widest points.
2. Pick a depth. Tap a preset (2, 3 or 4 inches) or type your own — 3 inches is the standard.
3. Press Calculate. Buy the rounded-up figure: cubic yards for bulk delivery, bags for small jobs.
4. For irregular beds, split the bed into rectangles, run each section, and add the totals.

Depth is the one setting that matters — too thin and weeds walk through, too thick and you suffocate the soil:

Never pile mulch against tree trunks or plant stems. The "mulch volcano" traps moisture against bark, inviting rot and pests — keep mulch 3–6 inches back from trunks, a rule emphasized in university mulching guidance such as University of Minnesota Extension. Poured borders and edging use the same cubic-yard math as mulch — a concrete calculator handles slabs and footings.

Bagged mulch is usually sold in 2 cu ft bags (some brands use 3 cu ft). One cubic yard is 27 cu ft — that is 13.5 two-cubic-foot bags, so think of a yard as roughly 14 bags.

Rule of thumb: below about 2–3 cubic yards, bags are simpler — no delivery fee, no driveway pile. Above that, bulk delivery usually costs roughly half as much per yard, but factor in the delivery fee and the wheelbarrow work to move it.

The expensive errors are all avoidable:

• Ordering the exact volume. Beds are never perfectly level and mulch settles — always round up. You cannot buy half a bag or half a yard.
• Going deeper than 4 inches around plants. Thick mulch turns hydrophobic, shedding water instead of absorbing it, and starves roots of oxygen.
• Volcano mulching trees. Mulch piled against the trunk rots the bark; keep a 3–6 inch mulch-free ring.
• Never refreshing. Organic mulch decomposes into the soil — top up once a year or when the layer drops below about 2 inches.

Measure the bed properly rather than eyeballing it: a "roughly 10 by 10" guess that is really 12 by 11 nearly doubles the volume.