How Much Soil Do I Need for a Raised Bed?
Multiply length × width × depth. A 4 × 8 ft bed, 12 in deep, holds 32 cu ft of soil (about 1.2 cu yd); with 10% for settling, buy about 35 cu ft, or 18 bags of 2 cu ft. A 1.2 × 2.4 m bed, 300 mm deep, holds 864 litres; with settling, about 950 litres or 20 bags of 50 litres.
Soil for common bed sizes
"With settling" adds 10%, because loose soil compacts once it's watered.
| Bed | Volume | With settling | Cubic yards | 2 cu ft bags |
|---|---|---|---|---|
| 4 × 4 ft, 6 in deep | 8 cu ft | 8.8 cu ft | 0.33 cu yd | 5 |
| 4 × 4 ft, 12 in deep | 16 cu ft | 17.6 cu ft | 0.65 cu yd | 9 |
| 4 × 8 ft, 6 in deep | 16 cu ft | 17.6 cu ft | 0.65 cu yd | 9 |
| 4 × 8 ft, 12 in deep | 32 cu ft | 35.2 cu ft | 1.3 cu yd | 18 |
| 4 × 8 ft, 18 in deep | 48 cu ft | 52.8 cu ft | 1.96 cu yd | 27 |
| 3 × 6 ft, 12 in deep | 18 cu ft | 19.8 cu ft | 0.73 cu yd | 10 |
| 2 × 8 ft, 12 in deep | 16 cu ft | 17.6 cu ft | 0.65 cu yd | 9 |
| Bed | Volume | With settling | 50 L bags |
|---|---|---|---|
| 1.2 × 1.2 m, 300 mm deep | 432 L | 475 L | 10 |
| 1.2 × 2.4 m, 300 mm deep | 864 L | 950 L | 20 |
| 1 × 2 m, 300 mm deep | 600 L | 660 L | 14 |
| 1.2 × 2.4 m, 450 mm deep | 1,296 L | 1,426 L | 29 |
Worked example
- A 4 × 8 ft bed, 12 in deep: 4 × 8 × 1 = 32 cu ft.
- Add 10% for settling: 35.2 cu ft.
- In bags of 2 cu ft: 35.2 ÷ 2 = 17.6, so 18 bags.
- In cubic yards: 35.2 ÷ 27 = 1.3 cu yd, so a bulk order of 1.5 yards.
Filling with a mix
Many gardeners fill raised beds with a blend of topsoil and compost rather than one material. To work out each, split the depth: for a 12 in bed that's two-thirds topsoil and one-third compost, calculate 8 in of topsoil and 4 in of compost. The topsoil calculator lets you switch between topsoil and compost.
Common mistakes
- Using the board height instead of the soil depth. If you plan to leave a rim above the soil, enter the soil depth.
- Forgetting a base layer. If you put cardboard or coarse material in the bottom, subtract its depth.
- Buying exactly the volume. Soil settles, so beds filled level sink after the first few waterings.
