How much soil for a 4×8 raised bed 18 inches deep?
A 4 × 8 ft raised bed 18 inches tall, filled to 1 inch below the rim, holds 45.3 cubic feet of soil (1.68 cubic yards). With 10% for settling, plan on 49.9 cubic feet, or 34 bags of 1.5 cu ft.
How to work it out
- Soil depth: 18 in bed − 1 in below the rim = 17 in
- 8 ft × 4 ft × 17 in ÷ 12 = 45.3 cu ft (bed volume)
- 45.3 cu ft + 10% for settling = 49.9 cu ft
- 49.9 cu ft ÷ 1.5 cu ft per bag = 34 bags
Taller beds are easier on the back and knees but use 50% more soil than a 12 in bed. That extra depth is where many gardeners put logs, branches or leaves in the bottom third to cut the cost; most vegetable roots do their work in the top foot, so they rarely need a full 18 in of purchased mix.
Adjust for your project
More options: Settling · Mix · Bag price …
- Soil depth (filled)
- 17 in
- Soil to buy
- 49.9 cu ft (1.85 cu yd)
- Or order bulk garden blend
- 2 cubic yards
- For beds deeper than about 12 in, some gardeners fill the bottom with logs, branches or leaves to cut the soil bill — see the guide on filling a raised bed cheaply.
DIY mix for a 4×8 bed 18 in tall, by recipe
| Recipe | Topsoil / screened garden soil | Compost | Perlite | Peat moss or coir | Vermiculite |
|---|---|---|---|---|---|
| 60 / 30 / 10 | 29.9 cu ft | 15 cu ft | 4.99 cu ft | 0 cu ft | 0 cu ft |
| 50 / 50 topsoil & compost | 24.9 cu ft | 24.9 cu ft | 0 cu ft | 0 cu ft | 0 cu ft |
| Equal thirds (Mel’s Mix) | 0 cu ft | 16.6 cu ft | 0 cu ft | 16.6 cu ft | 16.6 cu ft |
What to know about a 4×8 raised bed 18 inches deep
Three courses of 2×6 lumber make a frame about 16½ in tall, so an "18 inch" wooden bed often holds 15–16 in of soil once you leave room below the rim. Measure the inside height of your frame and enter that; the calculator takes off the inch below the rim.
Soil pushes outward, and the push grows with depth. Oregon State University Extension recommends reinforcing beds longer than about 6 ft; at 18 in tall, add a stake or a cross-brace at the middle of each 8 ft side, or the boards will bow within a season or two.
If you fill the bottom 6 in with wood, leaves or other organic material and buy soil only for the rest (11 in, up to an inch below the rim), you are back to the same 32.3 cubic feet as a 12 in bed. Expect that kind of fill to sink more as it rots, and top up with compost each year. The cheap-filling guide walks through the layering options.
Buying it all as soil? At 49.9 cu ft, a 2-yard bulk order covers one bed with a little to spare; in bags it is 34. For the standard height, see How much soil for a 4×8 raised bed. A narrower 3×6 bed at 18 in holds just under a cubic yard.
Different size? Use the full Raised Bed Soil Calculator.
What you’ll need
- Galvanized metal raised bed kitMid-range price
Long-lasting and quick to assemble. Check the height — many kits are 12–17 in tall, which changes how much soil you buy.
See options on Amazon (opens in a new tab) - Wheelbarrow (6 cu ft class)Mid-range price
Most home wheelbarrows hold 4–6 cubic feet — so a cubic yard of mulch is five or six trips. Two wheels are steadier on soft ground.
See options on Amazon (opens in a new tab) - Compost bin or tumblerMid-range price
Turns yard waste into the compost the calculators keep telling you to buy. Tumblers are tidier; open bins handle more volume.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How much soil to buy for a 4×8 bed 18 inches deep if the bottom 6 inches is logs?
About 32.3 cubic feet for the 11 inches of soil above the logs (22 bags of 1.5 cu ft), about a third less than filling the whole bed with soil.
How much soil for a 4×8 raised bed 24 inches deep?
67.5 cubic feet filled to an inch below the rim, with 10% for settling (2.5 cubic yards), or 45 bags of 1.5 cu ft. A bed this tall is a strong case for filling the bottom with wood or leaves.
How many 2 cu ft bags of soil for a 4×8 bed 18 inches deep?
25 bags of 2 cu ft for 49.9 cubic feet.
Other common sizes
- How much soil for a 4×8 raised bed — 32.3 cu ft
- How much soil for a 4×4 raised bed — 16.1 cu ft
- How much soil for a 3×6 raised bed — 18.2 cu ft
- How much soil for a 2×8 raised bed — 16.1 cu ft
- How much soil for a 1.2 × 2.4 m raised bed — 871 L
Sources
- University of Minnesota Extension: Raised bed gardens (opens in a new tab) — Soil blend of roughly 1/2–2/3 topsoil and 1/3–1/2 plant-based compost; too much compost holds excess water.
- University of Missouri Extension: Raised-Bed Gardening (G6985) (opens in a new tab) — Four feet is a convenient width; about 3 ft if reached from one side; most plants need a 6–12 in rooting zone.
- Oregon State University Extension: Raised bed gardening (FS 270) (opens in a new tab) — Beds longer than about 6 ft should be reinforced so the soil doesn’t push the sides out.