How Much Soil to Fill a Raised Bed
Multiply length by width in feet by depth in inches, then divide by 12 for cubic feet. Divide by 27 for cubic yards. A 4 by 8 foot bed 12 inches deep take...
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How Much Soil to Fill a Raised Bed
A 4 by 8 foot bed filled 12 inches deep needs 32 cubic feet of soil. That is about 1.2 cubic yards, or 16 bags of 2 cubic feet.
Enter your own beds on the Raised Bed Desk. It does the math, splits it into topsoil and compost, and counts bags.
The Formula
- Length in feet times width in feet gives square feet.
- Times depth in inches, divided by 12, gives cubic feet.
- Divide cubic feet by 27 for cubic yards.
- Divide cubic feet by the bag size on the label for the number of bags.
Example: 4 ft x 8 ft = 32 sq ft. 32 x 12 in / 12 = 32 cu ft. 32 / 27 = 1.19 cu yd.
Common Bed Sizes
| 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 | 1.0 | 14 |
| 4 x 8 ft | 12 in | 32 | 1.2 | 16 |
| 4 x 8 ft | 18 in | 48 | 1.8 | 24 |
Add a little extra. New fill sinks as it is watered in, and you will top up the low spots after the first few weeks.
Bags or Bulk
- Under about 1 cubic yard: bags are easier to haul and store.
- 1 cubic yard or more: bulk by the cubic yard is usually much cheaper than bags, according to University of Minnesota Extension. Ask the supplier what the topsoil is made of and where it came from.
Topping Up an Old Bed
An existing bed only needs enough compost to replace what settled. One inch over a 4 by 8 foot bed is 2.7 cubic feet. Two inches is 5.3 cubic feet. Heavy compost every year builds up phosphorus and salts, so base it on a soil test every 2 to 3 years. See the Soil Test Desk.
Related
Sources: University of Minnesota Extension, Raised bed gardens; Utah State University Extension, Raised Bed Gardening.