How to calculate compost
Cubic feet = Area (sq ft) × Depth (in) ÷ 12
Cubic yards = Cubic feet ÷ 27
Cubic yards = Cubic feet ÷ 27
Worked example
Adding 2 in of compost to a 20 × 10 ft vegetable bed: 200 × 2 ÷ 12 = 33.3 cubic feet. That's about 1.25 cubic yards, or 34 bags of 1 cubic foot.
How much compost to use
| Use | Depth | Compost per 1,000 sq ft |
|---|---|---|
| Top-dressing a lawn | ¼ in | 0.8 yd³ |
| Top-dressing after aeration | ½ in | 1.5 yd³ |
| Yearly top-up for beds | 1 in | 3.1 yd³ |
| New garden bed, mixed into soil | 2–3 in | 6.2–9.3 yd³ |
Tips
- For new beds, spread compost and dig or till it into the top 6–8 in of soil.
- For lawns, rake a thin layer into the grass so the blades still show. Too thick a layer smothers the lawn.
- Bagged compost is often sold by volume (1 ft³ or 0.75 ft³) and sometimes by weight (40 lb). A 40 lb bag is usually about 0.75 ft³.
Frequently asked questions
How much compost do I need for a 4 × 8 raised bed?
For a 2 in top-up, about 5.3 cubic feet, or 6 bags of 1 ft³. To fill a new 12 in bed with a 40% compost mix, you need about 13 cubic feet of compost.
How many bags of compost are in a yard?
27 bags of 1 cubic foot, or 36 bags of 0.75 cubic feet.
How thick should compost be on a lawn?
Spread ¼–½ in after aeration or overseeding. That works out to about 0.8–1.5 cubic yards per 1,000 sq ft.
Last reviewed 2026-11-14. Material weights are typical industry averages and vary by supplier, moisture and compaction.