Compost Calculator: Cubic Yards for Top Dressing
How much compost do you need to spread over a lawn or bed? Enter the area, the depth of the compost layer and a little extra for uneven ground. You get cubic yards, feet and metres, the bags to buy, and the cubic yards per acre. After switching units, re-enter your measurements.
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Formula
volume (ft3) = area (ft2) x depth (in) / 12 x (1 + extra %)cubic yards = ft3 / 27;m3 = ft3 x 0.028316846592bags = round up (ft3 / 1)for bags of 1 cubic footyards per acre = 43,560 x depth (in) / 12 / 27(about 134.44 per inch of depth)
Worked example
1,000 ft2 at 1 in deep with 10% extra:
- 1,000 x 1 / 12 = 83.33 ft3; x 1.10 = 91.67 ft3
- 91.67 / 27 = 3.40 yd3 (2.60 m3)
- 91.67 / 1 = 91.67, so 92 bags
- Per acre at 1 in: 43,560 / 12 / 27 = 134.44 yd3
Second case: a 4x8 ft bed (32 ft2) top-dressed 2 in deep. 32 x 2 / 12 = 5.33 ft3, and with 10% extra 5.87 ft3 (0.22 yd3), so 6 bags.
When to use it
Use it when you are spreading finished compost on top of existing soil: lawn top dressing, refreshing beds each spring, or feeding a vegetable plot. Typical depths are about 1/4 to 1/2 inch on lawns and 1 to 2 inches on beds. These are typical values, so follow the advice for your own plants.
Common mistakes
- Entering depth in feet or centimetres while the unit is imperial. Depth is in inches or centimetres.
- Forgetting the extra for uneven ground, then running short.
- Reading the per-acre figure as including the extra percentage; it does not.
How it differs from nearby calculators
This page sizes a layer of finished compost on the surface. The compost ratio calculator is a different tool: it balances carbon and nitrogen in a compost pile before it is made. To fill a new bed use the raised bed soil calculator, and for loose soil or mulch use the topsoil and mulch calculators.
Assumptions
- Bags hold 1 cubic foot (a typical retail size; check the label).
- Metric inputs are converted exactly (1 ft = 0.3048 m, 1 in = 2.54 cm).
Frequently asked questions
How much compost do I need for 1,000 square feet?
A layer 1 inch deep over 1,000 square feet is 1,000 / 12 = 83.3 cubic feet, or 3.09 cubic yards. With 10 percent extra it is 91.7 cubic feet, or 3.40 cubic yards, which is 92 bags of 1 cubic foot.
How deep should I spread compost?
Typical top-dressing depths are about 1/4 to 1/2 inch on lawns and 1 to 2 inches on vegetable and flower beds. Deeper layers are sometimes dug in when making a new bed. These are typical values; follow the advice for your plants and soil.
How many cubic yards of compost per acre?
One acre is 43,560 square feet. At 1 inch deep that is 43,560 / 12 / 27 = 134.4 cubic yards, and at 2 inches it is 268.9. The per-acre figure ignores the extra percentage.
Is compost the same as topsoil or mulch?
No. Compost is decomposed organic matter that feeds the soil, topsoil is mineral soil used to fill and level, and mulch is a surface covering to hold moisture. This page sizes a compost layer; use the topsoil or mulch calculators for those materials.
How much compost do I need for a 4x8 raised bed?
A 4x8 bed is 32 square feet. A 2 inch layer of compost is 32 x 2 / 12 = 5.33 cubic feet, and with the default 10 percent extra it is 5.87 cubic feet, or 6 bags of 1 cubic foot. Filling a new bed with soil is a different job; use the raised bed soil calculator for that.
How much compost do I need to top-dress a lawn?
Lawns usually get a thin layer, about 1/4 to 1/2 inch (a typical range). For 1,000 square feet at 1/2 inch with no extra that is 1,000 x 0.5 / 12 = 41.67 cubic feet, or 1.54 cubic yards.
How many cubic yards of compost for 100 square metres?
Choose metric units, enter 100 for the area and 3 for the depth in centimetres. The tool converts exactly and gives 116.54 cubic feet, which is 4.32 cubic yards or 3.30 cubic metres, with 10 percent extra.