Calculators · Compost Calculator
LandscapingCompost Calculator
Choose how you will use compost, enter the area and layer thickness, and get cubic yards, bags and weight.
Compost needed
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How to calculate how much compost you need
Compost is sold by the cubic yard in bulk and by the cubic foot in bags. The volume is the area times the thickness of the layer, and a cubic yard is 27 cubic feet.
| Step | Formula |
|---|---|
| 1. Square feet | length (ft) × width (ft). For a circle, 3.1416 × (diameter ÷ 2)² |
| 2. Cubic feet | square feet × thickness (in) ÷ 12 |
| 3. Cubic yards | cubic feet ÷ 27, or square feet × thickness (in) ÷ 324 |
| 4. Bags | cubic feet ÷ cubic feet per bag, rounded up |
| 5. Raised bed or mix | bed volume × share of compost (%) ÷ 100 |
Use one area for each lawn, bed or border. Measurements like 10'6" work too, and so do inches, yards and meters. The extra box adds an allowance to the compost only.
How thick should compost be?
It depends on how you use it. The sources below are a recycling association, compost producers and a group of water utilities, so these are practical guides and not a code. Checked October 2026.
| Use | Thickness or share | Source |
|---|---|---|
| Lawn topdressing | 1/4 to 1/2 in of fine compost | Michigan Recycling Coalition, McGill, The Compost Company |
| Topdressing around trees, shrubs, flowers and vegetables | 1 to 2 in | Michigan Recycling Coalition |
| Mulch | 2 to 3 in (The Compost Company), 1 to 3 in (Saving Water) | The Compost Company, Saving Water Partnership |
| Worked into the soil | 1 to 2 in mixed 6 to 8 in deep | Michigan Recycling Coalition, McGill |
| New planting beds | 2 to 4 in worked into the top 6 to 8 in | The Compost Company |
| Soil amendment before planting | 1 to 3 in, 3 for sandy soil and 1 to 2 for heavy clay | Saving Water Partnership |
| New topsoil mix | 20 to 30% compost, 70 to 80% subsoil | Michigan Recycling Coalition |
| Soil blend, raised beds and containers | at most 25 to 30% in a blend, no more than 25% in raised beds and containers | McGill |
| Amending native soil | 1 part compost to 2 to 3 parts soil | The Compost Company |
Example: topdressing a lawn
A lawn measures 1,000 square feet and you spread 1/2 inch of compost. The compost comes in bags of 1 cubic foot and weighs 1,150 pounds per cubic yard in the WSU Extension guide.
| Step | Operation | Result |
|---|---|---|
| Cubic feet | 1,000 × (0.5 ÷ 12) | 41.67 ft³ |
| Cubic yards | 41.67 ÷ 27 | 1.54 yd³ |
| Bags of 1 cu ft | 41.67 rounded up | 42 bags |
| Pounds | 1.5432 × 1,150 | 1,775 lb |
| Short tons | 1,775 ÷ 2,000 | 0.89 tons |
With the GoodGravel range of 1,600 to 2,200 pounds per cubic yard the same job weighs 2,469 to 3,395 pounds, or 1.23 to 1.70 tons. The volume does not change, only the weight.
Example: a raised bed
A raised bed is 4 ft by 8 ft and 12 inches deep. Pick “Blend into a bed mix” and type 25% compost, a share inside the Michigan Recycling Coalition range and within McGill’s limit for raised beds.
| Step | Operation | Result |
|---|---|---|
| Bed volume | 4 × 8 × (12 ÷ 12) | 32.00 ft³ |
| Compost | 32 × 25% | 8.00 ft³ |
| Compost in cubic yards | 8 ÷ 27 | 0.30 yd³ |
| Bags of 1 cu ft | 8 ÷ 1 | 8 bags |
| Other soil | 32 − 8 = 24 ft³ ÷ 27 | 0.89 yd³ |
How much compost for common areas?
Cubic yards of compost, from square feet × thickness in inches ÷ 324.
| Area | 1/4 in | 1/2 in | 1 in | 2 in | 3 in |
|---|---|---|---|---|---|
| 100 ft² | 0.08 | 0.15 | 0.31 | 0.62 | 0.93 |
| 500 ft² | 0.39 | 0.77 | 1.54 | 3.09 | 4.63 |
| 1,000 ft² | 0.77 | 1.54 | 3.09 | 6.17 | 9.26 |
| 5,000 ft² | 3.86 | 7.72 | 15.43 | 30.86 | 46.30 |
How many bags of compost are in a cubic yard?
The number of bags is 27 divided by the cubic feet on the bag. The sizes in the first column are the ones in the Saving Water Partnership calculator, and McGill and The Compost Company count 1 cubic foot bags. Bag sizes vary by brand, so read your label.
| Bag size | Bags per cubic yard | One bag covers at 1/2 in | One bag covers at 1 in |
|---|---|---|---|
| 1 cu ft | 27 | 24 ft² | 12 ft² |
| 1.5 cu ft | 18 | 36 ft² | 18 ft² |
| 2.2 cu ft | 12.3 | 52.8 ft² | 26.4 ft² |
| 2.5 cu ft | 10.8 | 60 ft² | 30 ft² |
| 3 cu ft | 9 | 72 ft² | 36 ft² |
How much does a cubic yard of compost weigh?
A Washington State University Extension guide for farmers (WSU Snohomish County Extension, working draft of January 2016) assumes about 1,150 pounds per cubic yard at 50 percent moisture. It also shows a lab data sheet at 39 pounds per cubic foot, which is 1,053 pounds per cubic yard. GoodGravel, an information site on landscape materials, lists 1,600 to 2,200 pounds. The two do not overlap, so the weight is the least certain number on this page. If your supplier gives the bulk density of the compost you are buying, choose “Custom density” and type it.
Tips for ordering
- Buy bulk by the cubic yard for big jobs. Use bags for small beds, and count them from the cubic feet printed on the label.
- Use the thin layers for lawns and the thicker ones for beds.
- Soil to mix with the compost? Estimate it with the topsoil calculator. For bark or wood mulch, see the mulch calculator.
- To convert a weight into volume and back, use the tons to cubic yards converter.
Frequently asked questions
How do I calculate how much compost I need?
Multiply the length of the area by its width to get square feet. Multiply by the thickness in inches and divide by 324 to get cubic yards. A 10 ft by 10 ft bed with 1 inch of compost is 100 × 1 ÷ 324 = 0.31 cubic yards, or 8.3 cubic feet. Divide the cubic feet by the size of your bag to count bags.
How much compost do I need for 100 or 1,000 square feet?
For 100 square feet you need 0.08 cubic yards at 1/4 inch, 0.15 at 1/2 inch, 0.31 at 1 inch and 0.62 at 2 inches. For 1,000 square feet the figures are ten times larger, 0.77 cubic yards at 1/4 inch, 1.54 at 1/2 inch, 3.09 at 1 inch and 6.17 at 2 inches. Lawn topdressing uses the thin layers and beds use the thicker ones.
How much does a 40 lb bag of compost cover?
A weight is not a volume, so use the cubic feet printed on the bag. A bag of 1 cubic foot covers 12 square feet at 1 inch, 24 square feet at 1/2 inch and 48 square feet at 1/4 inch. If compost weighs about 1,150 pounds per cubic yard, which is 42.6 pounds per cubic foot, then 40 pounds is about 0.94 cubic feet.
How much compost do I need for a raised bed?
Choose “Blend into a bed mix”, type the depth of the bed and the share of compost. A 4 ft by 8 ft bed filled 12 inches deep is 32 cubic feet. At 25 percent compost that is 8 cubic feet of compost, or 0.30 cubic yards, and 24 cubic feet of other soil. McGill says no more than 25 percent compost in raised beds or containers, and the Michigan Recycling Coalition recommends 20 to 30 percent in new topsoil.
How thick should a layer of compost be?
The sources we checked in October 2026 say 1/4 to 1/2 inch of fine compost on lawns, 1 to 2 inches around trees, shrubs, flowers and vegetables, and 1 to 2 inches mixed 6 to 8 inches deep into garden soil. The Compost Company suggests 2 to 3 inches as mulch and Saving Water Partnership says 1 to 3 inches, using 3 for sandy soil and 1 to 2 for heavy clay.
How much does a cubic yard of compost weigh?
The two sources we found do not agree. A Washington State University Extension guide uses about 1,150 pounds per cubic yard at 50 percent moisture, and GoodGravel lists 1,600 to 2,200 pounds. Moisture and the ingredients change the number, so ask your supplier. Pick the figure in the dropdown or choose “Custom density”.
Does this calculator work out a compost recipe?
No. It tells you how much finished compost to buy or spread. A recipe for building a pile, with a carbon to nitrogen ratio, is a different kind of calculator.
More calculators
- Topsoil Calculator Calculate the cubic yards and tons of topsoil for a lawn, raised bed or garden.
- Mulch Calculator Find how many cubic yards or bags of mulch cover your garden beds at the depth you want.
- Tons to Cubic Yards Calculator Convert tons to cubic yards (and back) for gravel, topsoil, asphalt and your own density.