How this calculator works
The calculator multiplies bed area by spread depth to find volume, then converts that volume to cubic yards for bulk compost and the bag volume you select. It rounds bag purchases up to whole bags; the optional price is your own planning estimate.
For a 20 ft × 10 ft bed at 2 inches, the calculator uses 200 × (2 ÷ 12) = 33.3 cubic feet. Divide by 27 for 1.23 cubic yards, or round 33.3 ÷ 1.5 up to 23 bags.
Choose depth, then buy by volume
A 1–2 inch top dressing is a common planning range for established beds; work a deeper amendment into a new bed only when it fits the planting plan. Bulk compost is commonly sold by the cubic yard, while bags list a cubic-foot volume. Use the bag's printed volume—not its weight—to compare it with this calculator, because bag weights vary with moisture and product. Measure separate beds individually, add the volumes, and round bulk orders according to the supplier's delivery increment. For a new raised bed, calculate its fill separately; for a surface cover, use the mulch calculator.
Frequently asked questions
How many bags of compost are in a cubic yard?
A cubic yard is 27 cubic feet, so it takes 18 bags at 1.5 cubic feet each. Always check the volume printed on your chosen bag.
How deep should I spread compost?
For an established bed, a 1–2 inch top dressing is a practical planning range. Select the depth that fits your soil and planting plan.
Should I buy compost by the bag or cubic yard?
Compare both options by volume. Divide the bulk price by 27 for a cost per cubic foot, then compare it with the bag's listed cubic-foot volume, including any delivery charge.