How it works
The calculator multiplies the area by the depth of the compost layer, adds any extra you enter, and divides by the bag size if you give one.
Area = Length × Width
Volume = Area × Compost depth × (1 + Extra ÷ 100)
Bags = ⌈ Volume ÷ Bag size ⌉
⌈ ⌉ means rounding up to the next whole bag. In US units this is square feet × depth in inches ÷ 324 = cubic yards, since a cubic yard is 27 cubic feet and a foot is 12 inches. The two depth presets follow Virginia Cooperative Extension: about 2 inches worked into a bed or new lawn, up to 1/4 inch as a lawn topdressing. Units are converted internally, so an area in feet with a depth in inches, or square meters with centimeters, works directly.
Worked example
Inputs
- Measure by
- Length × width
- Area length
- 20 ft
- Area width
- 10 ft
- Use
- Work into the soil (beds, new lawns)
- Compost depth
- 2 in
- Extra
- 0 %
Result
- Compost volume
- 1.23 cu yd (33.33 cu ft)
- Area covered
- 200 sq ft
Common mistakes
- Entering the topdressing depth in feet instead of inches. A quarter of an inch is 1/48 of a foot – the wrong unit orders far too much.
- Ordering by the depth you will till to. Two inches of compost worked into the top six inches of soil is a 2 in layer, not 6 in.
- Spreading a thick layer on an established lawn. Extension services advise thin layers of 1/4 to 1/2 inch, repeated over time.
- Comparing bag and bulk prices without converting. One cubic yard is 27 cubic feet, or about 0.76 cubic meters.
Assumptions and limits
- The area is a rectangle, or you have entered its total area, and the layer is the same depth everywhere.
- The volume is area × depth plus any extra you enter. Compost settles and is compacted when it is worked in; that is covered only by the extra.
- The depths shown are example values from extension guidance, not a recommendation for your soil – a soil test and your local extension service can tell you more.
- Bags are rounded up to whole bags. The bulk volume is not rounded.
Frequently asked questions
How much compost do I need for 1,000 square feet?
At 1/4 inch, 1,000 × 0.25 ÷ 324 = 0.77 cubic yards, about 21 cubic feet. At 1 inch it is 3.09 cubic yards, and at 2 inches 6.17 cubic yards.
How deep should I spread compost?
For a bed or a new lawn, extension services suggest a layer of about 1 to 2 inches worked into the top 6 to 8 inches of soil. For an existing lawn, a topdressing of 1/4 inch, and no more than 1/2 inch at a time.
How many square feet does a cubic yard of compost cover?
324 sq ft at 1 inch deep, 162 sq ft at 2 inches and 1,296 sq ft at 1/4 inch. Nebraska Extension rounds the 1 inch figure to 325 sq ft.
How many bags of compost make a cubic yard?
Divide 27 cubic feet by the bag size. With 1 cubic foot bags that is 27 bags; with 2 cubic foot bags, 13.5, so 14.
How do I convert cubic yards of compost to cubic meters?
Multiply by 0.7646. The calculator shows the volume in either system when you switch units.
Sources
- Using Compost in Your Landscape (Publication 426-704, 2021) — Virginia Cooperative Extension, Virginia Tech. "Spread about 2 inches of compost over the planned lawn area. Till this into the soil"; "Topdressing existing lawns with up to 1/4 inch depth of quality compost 1 to 2 times per year"; gardens: "spread about 2 inches … and work it 6 to 8 inches into the soil". Defaults 2 in worked in, 1/4 in topdressing.
- Topdressing a Home Lawn (Home & Garden Information Center fact sheet, 2020) — Clemson Cooperative Extension. "Topdressing applications should be light with no more than ½- inch of material applied at a time" – the threshold of the thick-topdressing note.
- Uses of Compost in the Landscape — Nebraska Extension in Lancaster County. "To amend bare soil, cover the area with 1 to 2 inches of compost and incorporate it by tilling the upper six inches of the soil. One cubic yard of compost will cover 325 sq. ft. at a depth of 1 inch"; lawns: "apply a ¼ to ½-inch layer of fine compost" after aerating.
- NIST Handbook 44, Appendix C – General Tables of Units of Measurement — National Institute of Standards and Technology. Exact unit definitions: 1 in = 2.54 cm, 1 yd³ = 27 ft³, 1 US gal = 231 in³, 1 lb = 0.45359237 kg.
Method reviewed November 6, 2026