How much soil for your raised bed?
Soil for one or several raised beds in cubic feet, yards, liters and bag counts, with settling and a 60/30/10 topsoil-compost-aeration breakdown.
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Before you buy: A "2×6" board is really 5.5" tall, so two stacked boards make an 11" bed, not 12". That is why the default depth is 11".
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Worked examples
| Bed | Soil (+15%) | 1.5 ft³ bags |
|---|---|---|
| 8×4 ft, 11" deep | 33.7 ft³ | 23 |
| 6×3 ft, 10" deep | 17.3 ft³ | 12 |
| 4×4 ft, 12" deep | 18.4 ft³ | 13 |
| 12×4 ft, 11" deep | 50.6 ft³ | 34 |
| 8×2 ft, 18" deep | 27.6 ft³ | 19 |
Formula & assumptions
Volume (ft³) = length × width × (depth ÷ 12) × beds. Bagged and loose soil compresses after watering, so a 10–20% settling allowance is added. The 60/30/10 split (topsoil, compost, an aeration material such as perlite or pine bark fines) is one common blend; many gardeners use a 50/50 topsoil–compost blend instead, so use the total if you buy a premixed raised-bed soil.
FAQ
How many bags of soil for a 4x8 raised bed?
At 11 inches deep it holds 29.3 ft³. Add 15% for settling and you need about 33.7 ft³: 23 bags of 1.5 ft³ or 17 bags of 2 ft³.
Do I need to fill a tall raised bed all the way with soil?
No. For beds deeper than about 18 inches, many gardeners fill the bottom third with logs, branches or leaves (hügelkultur style) and top it with 12 inches of soil. Lower the depth input to the soil layer only.
Bags or bulk?
Above about 2 cubic yards (54 ft³), bulk delivery from a landscape yard usually costs less than bags, though delivery fees vary.
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