Raised Bed Desk: how much soil, compost, and cardboard you need
Enter your beds to get cubic feet, cubic yards, and bag counts for a new fill, a compost top-up, or a no-dig bed you layer this fall so it is ready to plant in spring. The desk can pull bed sizes from your saved garden layouts and check the depth your My Garden crops need. Your plan saves on your device. No account needed.
Free raised bed soil calculator. Enter bed length, width, and depth for cubic feet, cubic yards, and bag counts, split into topsoil and compost. Plan a compost top-up or a no-dig bed you build this fall with cardboard and leaves.
Soil for common bed sizes
Length times width in feet, times depth in inches, divided by 12, gives cubic feet. Divide by 27 for cubic yards.
| Bed | Depth | Cubic feet | Cubic yards | 2 cu ft bags |
|---|---|---|---|---|
| 4 x 4 ft | 6 in | 8 | 0.3 | 4 |
| 4 x 4 ft | 12 in | 16 | 0.6 | 8 |
| 3 x 6 ft | 12 in | 18 | 0.7 | 9 |
| 2 x 8 ft | 12 in | 16 | 0.6 | 8 |
| 4 x 8 ft | 6 in | 16 | 0.6 | 8 |
| 4 x 8 ft | 10 in | 26.7 | 1 | 14 |
| 4 x 8 ft | 12 in | 32 | 1.2 | 16 |
| 4 x 8 ft | 18 in | 48 | 1.8 | 24 |
What to fill it with
University of Minnesota Extension recommends about 1/2 to 2/3 loam or sandy loam topsoil and 1/3 to 1/2 plant-based compost. Utah State University Extension also lists equal parts topsoil, compost, and a drainage material such as coarse sand, perlite, pumice, or vermiculite. Do not fill a bed with potting soil, and use manure only when a soil test calls for phosphorus.
Build a no-dig bed this fall
Lay cardboard over mowed grass with edges overlapped at least 8 inches, then stack equal layers of greens and browns to 18 inches or more, ending with browns. Oregon State University Extension says fall is an excellent time because the bed breaks down over winter. Expect about six months before planting. Shredded fall leaves make the brown layers.
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