Compost Calculator
Find compost volume from the area you want to cover and your planned depth, then compare cubic yards with bag quantities.
How this calculator works
Measure the surface that will receive compost and enter the intended finished depth. For multiple beds, add their areas together or calculate each bed separately. A shallow topdressing and a deeper soil amendment use very different quantities; select the depth based on the gardening project and product guidance.
volume (cu ft) = area (sq ft) × depth (in) ÷ 12 cubic yards = volume ÷ 27 bags = ceil(volume ÷ bag volume)
Worked example
A 500 sq ft area covered 2 inches deep needs 500 × 2 ÷ 12 = 83.33 cu ft, or about 3.09 cu yd. With 1 cu ft bags, plan on 84 bags.
Understand the volume estimate
The result is geometric volume. Bulk material may settle or contain moisture, and delivery volume can vary, so ask the supplier how their product is measured. The bag count assumes each bag contains its stated volume and rounds up to full bags; it does not include an extra allowance for settling or uneven ground.
Check compost suitability
Compost products differ in texture, maturity, nutrient content, and intended use. Follow product directions for mixing or topdressing and avoid applying material in a way that covers plant crowns or conflicts with local guidance. This calculator estimates quantity, not soil nutrient needs.
Frequently asked questions
How many cubic yards of compost do I need?
Multiply the area in square feet by the depth in inches, divide by 12 to get cubic feet, then divide by 27 to convert to cubic yards.
How many bags of compost equal a cubic yard?
A cubic yard is 27 cubic feet. Divide 27 by the bag’s volume in cubic feet; for 1 cu ft bags that is 27 bags, and for 2 cu ft bags it is 13.5, so you would buy 14 whole bags.
How deep should compost be for topdressing?
The appropriate depth depends on the use, plants, and product. Enter the depth recommended for your specific application rather than using one depth for every garden.
Does this estimate include settling?
No. It calculates the placed geometric volume and does not model settling, compaction, or uneven surfaces. Ask a bulk supplier whether to add an allowance for their material.