How Much Soil Do You Need for a Raised Bed?
The simple math for filling a raised garden bed, a chart for common bed sizes in cubic feet, bags and cubic yards, and when to buy bulk soil instead of bags.
Raised beds take a surprising amount of soil. A single 4-by-8-foot bed a foot deep needs 32 cubic feet, more than a dozen big bags. Here’s how to figure out exactly what you need.
The formula
Length (ft) x Width (ft) x Depth (ft) = cubic feet of soil
Measure depth in feet: 6 inches is 0.5 ft, 10 inches is about 0.83 ft, 12 inches is 1 ft, 18 inches is 1.5 ft.
Then convert:
- Bags: divide cubic feet by the bag size (usually 1, 1.5 or 2 cubic feet).
- Cubic yards (bulk): divide cubic feet by 27.
Add about 10 to 20 percent to account for settling, especially with fluffy mixes.
Example
A 4 x 8 ft bed, 12 inches deep:
- 4 x 8 x 1 = 32 cubic feet
- With 15% extra for settling: about 37 cubic feet
- In 1.5 cu ft bags: about 25 bags
- In bulk: 37 / 27 = about 1.4 cubic yards
Soil chart for common bed sizes
| Bed size | Depth | Cubic feet | 1.5 cu ft bags | Cubic yards |
|---|---|---|---|---|
| 2 x 4 ft | 12 in | 8 | 6 | 0.3 |
| 3 x 6 ft | 12 in | 18 | 12 | 0.7 |
| 4 x 4 ft | 12 in | 16 | 11 | 0.6 |
| 4 x 8 ft | 6 in | 16 | 11 | 0.6 |
| 4 x 8 ft | 12 in | 32 | 22 | 1.2 |
| 4 x 8 ft | 18 in | 48 | 32 | 1.8 |
| 4 x 12 ft | 12 in | 48 | 32 | 1.8 |
Figures are before the extra 10 to 20 percent for settling. Bags rounded up.
Round and odd-shaped beds
- Round: 3.14 x radius (ft) x radius (ft) x depth (ft). A 4-foot-wide round bed 12 inches deep: 3.14 x 2 x 2 x 1 = about 12.6 cubic feet.
- L-shaped or hexagon: break it into rectangles and triangles and add them up, or use the bed maker’s stated volume.
Bags or bulk?
- Bags are easier for one or two small beds and for elevated planters.
- Bulk delivery by the cubic yard is usually far cheaper for several beds or anything over about 1 cubic yard. You’ll need a spot for the pile and a garden cart.
Save soil in tall beds
For beds 18 inches or deeper, you can fill the bottom with untreated logs, branches and leaves. Here’s what to put in the bottom of a raised bed.
What soil to use
A raised bed mix usually combines topsoil, compost and a light material like peat, coir or pine bark fines. Straight topsoil can compact; straight compost can be too rich and settle a lot.
Questions people ask
How deep should a raised bed be for vegetables? At least 10 to 12 inches for most crops, deeper for carrots and potatoes.
How many bags of soil for a 4x8 raised bed? About 22 bags of 1.5 cubic feet for 12 inches deep, plus extra for settling.
How much is a cubic yard of soil? 27 cubic feet, enough to fill a 4 x 8 ft bed about 10 inches deep.
See our picks for the best raised garden beds for vegetables.