Free Compost Calculator
Use this compost calculator to see how much compost to buy for your lawn or garden beds.
Compost improves soil structure and feeds plants. It is usually spread in a thin layer on top of beds or lawns, or dug into new beds.
Bulk compost is sold by the cubic yard; bags are usually 1 or 2 cubic feet.
Compost example: top-dressing a lawn
Top-dressing a 1,000 sq ft lawn at 1/2 in: 1,000 sq ft × 0.5 in ÷ 12 = 41.7 cu ft, plus 5% extra = 43.8 cu ft. Divide by 27 to get 1.62 cubic yards, which weighs about 0.81 tons, or 22 × 2 cu ft bags.
How deep should compost be?
| Use | Depth | Notes |
|---|---|---|
| Top-dressing a lawn | 1/4 to 1/2 in | Rake it in so the grass blades show. |
| Feeding existing beds | 1 to 2 in | |
| Preparing new beds | 2 to 3 in | Dig into the top 6 to 8 in of soil. |
| Raised bed mix | About 40% of the bed | The rest is topsoil. |
Coverage per cubic yard and per bag
| Depth | Sq ft per cubic yard | Sq ft per 2 cu ft bag |
|---|---|---|
| 0.5 in | 648 | 48 |
| 1 in | 324 | 24 |
| 2 in | 162 | 12 |
| 3 in | 108 | 8 |
Buying tips
- A half-inch top-dressing on 1,000 sq ft of lawn needs about 1.5 cubic yards of compost.
- Ask whether bulk compost is screened. Screened compost spreads more evenly, especially on lawns.
- Compost weighs about half as much as topsoil, so a pickup can carry a full bed of it.
How much does compost weigh?
A cubic yard of compost typically weighs 800 to 1,400 lb (0.4 to 0.7 tons). The calculator uses 1,000 lb (0.5 tons) per cubic yard. Moisture and grading change the weight, so if your supplier sells by the ton, ask for their figure.
Frequently asked questions
How much compost do I need per square foot?
At 1 inch deep, each square foot needs 1/12 cu ft. One cubic yard covers about 324 sq ft at 1 inch.
How many bags of compost are in a yard?
27 bags of 1 cu ft, or 13.5 bags of 2 cu ft.
How much compost should I add to a raised bed?
A common mix is around 60% topsoil to 40% compost. For a 4 × 8 bed 12 inches deep (32 cu ft), that is about 13 cu ft of compost.
How accurate is this compost calculator?
The compost calculator gives the exact volume for the measurements you enter, then adds 5% extra (you can change it). Weights use a typical 0.5 tons per cubic yard; real loads vary with moisture, so confirm with your supplier if you buy by the ton. Measure carefully: an error of one inch in depth changes a 3 inch layer by a third.
How the compost calculator works
Volume = area × depth. Each area is worked out from its shape (length × width, π × radius², or ½ × base × height), converted to square feet, multiplied by the depth in feet, and added up. Cubic feet ÷ 27 = cubic yards.The extra percentage is then added, and bag counts are rounded up to whole bags. See how we calculate for every figure we use.