Soil for a 3x8 Raised Bed 18 Inches Deep
How much soil for a 3x8 raised bed 18 inches deep: 36.0 cubic feet, which is 1.33 cubic yards, 18 bags of 2 cubic feet or 24 bags of 1.5 cubic feet.
Volume and tonnage calculator →The math
- Volume: 3 × 8 × (18 ÷ 12) = 36.0 cu ft.
- Cubic yards: 36.0 ÷ 27 = 1.33 yd³.
- Bags: 36.0 ÷ 2 = 18 bags (2 cu ft), or ÷ 1.5 = 24 bags (1.5 cu ft).
The topsoil calculator handles any bed size.
Related: Soil for a 4x8 Raised Bed 18 Inches Deep
Soil for a 3x8 bed at other depths
| Depth | Cubic feet | Cubic yards | 2 cu ft bags |
|---|---|---|---|
| 6 in | 12.0 | 0.44 | 6 |
| 8 in | 16.0 | 0.59 | 8 |
| 10 in | 20.0 | 0.74 | 10 |
| 12 in | 24.0 | 0.89 | 12 |
| 18 in | 36.0 | 1.33 | 18 |
| 24 in | 48.0 | 1.78 | 24 |
When bulk soil pays off
This bed is big enough that a bulk load of garden mix usually beats bags. Many yards sell a blended raised-bed mix of topsoil and compost by the yard.
Related: Soil for a 4x12 Raised Bed 18 Inches Deep
What to fill it with
A common home mix is roughly 60 percent topsoil and 40 percent compost, or equal parts topsoil, compost and a drainage material. Avoid filling with plain clay fill dirt, which packs hard.
Settling
New soil settles, often by 10 to 20 percent in the first season. Overfill slightly or plan to top up with compost next spring. Tall beds can be partly filled with logs or branches at the bottom to save soil (a hugelkultur approach).
Common mistakes
Many people underestimate settling, so beds end up low by the second season. Others pile soil or mulch against tree trunks and siding, which invites rot and insects. Wet, sticky soil should wait for a drier day before spreading.
Measuring accurately
Walk the area with a tape and sketch it. Break odd shapes into rectangles and circles. If you are topping up an existing bed or lawn, measure only the new depth, since adding a full depth on top of existing soil overbuys.
Questions people ask
How many bags of soil for a 3x8 raised bed?
About 18 bags of 2 cubic feet at 18 inches deep.
How many cubic feet in a 3x8x18 inch bed?
36.0 cubic feet.
How many yards of soil for a 3x8 raised bed?
About 1.33 cubic yards at 18 inches deep.
What soil mix is best for raised beds?
Topsoil blended with compost, roughly 60/40, is a common starting point.
Will raised bed soil settle?
Yes, often 10 to 20 percent in the first season.
Related guides
- How Much Does a Yard of Topsoil Cover?
- How Many Bags of Topsoil in a Yard? Size Chart
- Fill Dirt vs Topsoil: Differences, Uses and Tons to Order
- How Much Does a Yard of Dirt Weigh? Topsoil, Fill, Clay
- Soil for a 3x6 Raised Bed 18 Inches Deep
- Soil for a 3x8 Raised Bed 12 Inches Deep
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