Outdoor, Deck & Fence
Mulch Calculator
Cubic yards and bag counts for garden beds at the depth your plants actually need.
Inputs
Results
Adjust the inputs to see your result.
About this calculator
Mulch is specified by depth — 3 in for weed suppression in beds, 2 in for a top-up — and sold by the cubic yard in bulk or by the 2 cu ft bag. This calculator converts bed area and depth into both, so you can compare bulk delivery against bags honestly.
What this number means
Mulch is a volume purchase disguised as an area project: what you are really deciding is bulk versus bags. One cubic yard is 27 cu ft — that is 13.5 standard 2 cu ft bags — and the price crossover usually arrives at about one yard: below it, bags are cheaper and cleaner; above it, a bulk delivery wins even after the delivery fee.
The depth field is doing quiet, important work. Mulch at 2 in is a cosmetic top-up; at 3 in it suppresses most weed seed; at 4 in it starts to moderate soil temperature and moisture the way mulch is supposed to. The calculator shows coverage at your chosen depth so you can see exactly what an extra inch costs.
The formula
- Cubic yards = Area (sq ft) × Depth (in) ÷ 324
- Cubic feet = Cubic yards × 27
- Bags = Cubic feet ÷ bag size, rounded up
- Coverage check: 1 cu yd covers 324 sq ft at 1 in, 162 at 2 in, 108 at 3 in, 81 at 4 in
Worked example
A 4 × 20 ft flower bed at 3 in deep.
- Area = 80 sq ft → volume = 80 × 3 ÷ 324 = 0.74 cu yd (20 cu ft)
- Bagged: 20 ÷ 2 = 10 bags of 2 cu ft
- Bulk: order 1 cu yd — the minimum most yards deliver — and you have a little spare for the bed by the fence
Assumptions and limitations
- One rectangular bed per calculation. For several beds, total the areas first (the Square Footage Calculator helps) and run the total — depth and volume add linearly.
- Bagged mulch volumes are the manufacturer's nominal fill. Bags settle in transit; if a bed must finish exactly level, one spare bag is cheap insurance.
- Playground and path mulch compact over a season (10–15%). For those surfaces, add the compaction to your depth or plan a top-up.
- Trees and shrubs inside the bed displace a little mulch; at normal planting density the effect is inside the rounding of a bulk order.
Frequently asked questions
At 3 in deep: 100 × 3 ÷ 324 = 0.93 cu yd — call it 1 cu yd bulk, or 13 bags of 2 cu ft. At 2 in it drops to 0.62 cu yd (9 bags). Depth is the lever: an extra inch over 100 sq ft is a third of a yard.
13.5 bags of the standard 2 cu ft size — so 14 bags in practice. For 3 cu ft bags it is 9, and for 1.5 cu ft bags it is 18. That is the comparison to make against a bulk yard price.
Three inches for planted beds — enough to block most weed germination and hold moisture. Two inches is fine for an annual top-up over existing mulch. Four inches for brand-new beds over bare soil. Keep it a few inches away from trunks and stems regardless of depth.
Bulk wins above roughly one cubic yard even with delivery, and by a wide margin above two yards. Below a yard, bags are usually cheaper in total and far easier to handle. The calculator shows both figures from one measurement so you can compare honestly.
A 2 cu ft bag covers 12 sq ft at 2 in deep, 8 sq ft at 3 in, or 6 sq ft at 4 in. Bag labels print the 2 in figure, which is why beds always seem to need more bags than the label suggests.