Topsoil & Mulch Calculator
Find the cubic yards and bags of topsoil, mulch or compost for a bed at a chosen depth, with a cost estimate.
How it works
cubic feet = length × width × (depth ÷ 12) · cubic yards = cubic feet ÷ 27 · bags = cubic feet ÷ bag size
Topsoil, mulch and compost are all sold both in bags (cubic feet) and in bulk (cubic yards), so the calculator gives both. Volume is length by width by depth, with depth converted from inches to feet, and one cubic yard equals 27 cubic feet — that is nine 3 cu ft bags or thirteen-and-a-half 2 cu ft bags. Mulch is typically laid 2–3 in deep to suppress weeds and hold moisture, while new topsoil for a lawn or bed goes 4–6 in.
Worked example
A 20 × 8 ft bed at 3 in of mulch: 20 × 8 × (3 ÷ 12) = 40 cu ft ÷ 27 = 1.48 cubic yards. In 2 cu ft bags that is 40 ÷ 2 = 20 bags — well past where a bulk yard delivery is cheaper.
Frequently asked questions
How deep should I lay mulch versus topsoil?
Mulch works best at 2–3 in — enough to block light to weeds and slow evaporation without smothering roots. New topsoil for establishing a lawn or bed is usually 4–6 in so roots have room to develop.
Bags or bulk?
Bags are convenient for small beds and easy to carry, but bulk (by the cubic yard) is much cheaper per unit once you need more than about a cubic yard — roughly 13 or more bags. Delivery fees can tip the comparison, so compare totals.
How many bags in a cubic yard?
It depends on bag size: a cubic yard is 27 cubic feet, so that is 9 of the 3 cu ft bags, about 13.5 of the 2 cu ft bags, or 18 of the 1.5 cu ft bags.
Related calculators
Estimates only — add for waste and confirm against local building codes and supplier specs.