Mulch & Soil Calculator (Cubic Yards / Bags)
Calculate cubic yards and bags of mulch, soil, or gravel needed for a garden bed at your chosen depth.
What this calculates
Mulch, soil, and gravel are sold by cubic yard (bulk) or by 2 cubic-foot bag (retail). 1 cubic yard covers a lot — 100 sq ft at 3 inches deep. This calculator converts your area and target depth into both bulk and bagged quantities so you can pick the cheaper delivery option.
Formula & how it works
Volume (cubic feet) = area_sq_ft × (depth_inches ÷ 12). Cubic yards = cu ft ÷ 27. Bags (2 cu ft each, common retail size) = cu ft ÷ 2. Typical depths: 2–3 inches for mulch maintenance, 3–4 inches for fresh garden beds, 4–6 inches for new lawns.
Worked example
Garden bed 8 × 20 = 160 sq ft, 3 inches deep. Volume = 160 × 0.25 = 40 cu ft = 1.48 cu yd. In 2-cu-ft bags: 20 bags. Bulk delivery is usually cheaper above ~1 cu yd, plus less plastic waste. Below 0.5 cu yd, bags from the garden center make more sense.
Frequently asked questions
How often should I refresh mulch?
Most organic mulches need topping up annually — they decompose into the soil (which is good!). Apply 1-2 inches each spring on existing beds. Decorative rock and rubber don't decompose but pull weeds through over time.
What's the best depth?
2-3 inches suppresses weeds and retains moisture. More than 4 inches can suffocate plant roots and harbor pests. Less than 1 inch is mostly cosmetic.
Bulk delivery cost?
Typically $30-60 per cubic yard plus $50-100 delivery. A single yard usually beats 13 bags ($70-100). Bigger jobs (3+ yards) skew strongly toward bulk.
Should I till mulch in?
No. Mulch sits on top — that's the point. Tilling it in can lock up nitrogen as it decomposes. Only soil amendments and compost are tilled into the bed.