Compost Calculator — How Much Compost Do You Need?
Find how much compost to top-dress a bed or lawn, or to amend soil. Enter the area and depth, and this calculator gives the volume in cubic yards and the number of bags.
How to use this calculator
- Enter the bed or lawn area in feet.
- Choose a depth: 0.5–1 inch to top-dress an existing bed or lawn, 2–3 inches to amend a new bed before planting.
- Pick the bag size sold at your store, or read the cubic yards for bulk delivery.
- Top-dressing yearly builds soil without digging — just spread and let worms work it in.
The formula
Compost is sold by volume, like mulch and soil.
Volume (cubic feet) = area × depth (in) ÷ 12. Cubic yards = ÷ 27.
Bags = cubic feet ÷ bag size, rounded up. A cubic yard is about 18 bags of 1.5 cu ft.
Worked example
A 10 ft × 10 ft bed top-dressed 1 in deep with 1.5 cu ft bags.
Area = 100 sq ftVolume = 100 × (1 ÷ 12) = 8.33 cu ftBags = 8.33 ÷ 1.5 = 5.6 → 6 bags
A 100 sq ft bed at 1 in needs about 0.31 cubic yards of compost — 6 bags of 1.5 cu ft.
Frequently asked questions
How much compost do I need?
For top-dressing, 0.5–1 inch over the area; for amending a new bed, 2–3 inches worked in. A 100 sq ft bed at 1 inch needs about 8.3 cubic feet (6 bags of 1.5 cu ft).
How deep should I top-dress with compost?
A quarter to one inch is plenty for lawns and established beds, applied once or twice a year. Thicker layers can smother grass and roots.
How many bags of compost in a cubic yard?
A cubic yard is 27 cubic feet — about 18 bags of 1.5 cubic feet, or 27 bags of 1 cubic foot. Bulk delivery is usually cheaper above roughly one cubic yard.