Soil calculator for raised beds
A 4 × 8 ft raised bed filled 12 in deep holds 32 cubic feet (1.19 cubic yards) of soil. For a 2 to 1 mix, that's 29 bags of topsoil and 11 bags of compost.
How deep to fill a raised bed
Texas A&M AgriLife's guide to building a raised bed says 8 to 12 in of soil is usually enough, and that vegetable beds should be 12 to 18 in deep. Where the bed sits on concrete or another hard surface, roots can't reach the ground below, so the University of Maryland Extension asks for at least 8 in for leafy greens, beans and cucumbers and 12 to 24 in for peppers, tomatoes and squash.
| Bed | 6 in deep | 8 in deep | 12 in deep | 18 in deep |
|---|---|---|---|---|
| 2 × 4 ft | 4 cu ft (0.15 yd) | 5.3 cu ft (0.20 yd) | 8 cu ft (0.30 yd) | 12 cu ft (0.44 yd) |
| 3 × 6 ft | 9 cu ft (0.33 yd) | 12 cu ft (0.44 yd) | 18 cu ft (0.67 yd) | 27 cu ft (1.00 yd) |
| 4 × 4 ft | 8 cu ft (0.30 yd) | 10.7 cu ft (0.40 yd) | 16 cu ft (0.59 yd) | 24 cu ft (0.89 yd) |
| 4 × 8 ft | 16 cu ft (0.59 yd) | 21.3 cu ft (0.79 yd) | 32 cu ft (1.19 yd) | 48 cu ft (1.78 yd) |
| 4 × 10 ft | 20 cu ft (0.74 yd) | 26.7 cu ft (0.99 yd) | 40 cu ft (1.48 yd) | 60 cu ft (2.22 yd) |
| 4 × 12 ft | 24 cu ft (0.89 yd) | 32 cu ft (1.19 yd) | 48 cu ft (1.78 yd) | 72 cu ft (2.67 yd) |
| 5 × 10 ft | 25 cu ft (0.93 yd) | 33.3 cu ft (1.23 yd) | 50 cu ft (1.85 yd) | 75 cu ft (2.78 yd) |
What to fill it with
Neither extension service recommends filling a bed with one product alone. Over existing ground, Maryland suggests compost and purchased topsoil at 1 to 2 or 1 to 1. Texas A&M lists three common blends, three quarters topsoil and a quarter compost, two thirds and one third, or half and half, and notes that the more compost a blend has, the sooner the bed will need topping up as it breaks down. For vegetables it suggests a third each of topsoil, peat moss and sand or coarse perlite.
On a hard surface, Maryland suggests compost and a soilless growing mix half and half, adding topsoil only to beds at least 16 in deep and then no more than a fifth of the volume. It also warns that bags sold as "organic soil" usually contain no topsoil at all. Potting soil grows vegetables well, but Texas A&M finds it too expensive for filling large beds; it is the right choice for pots.
Area: 8 ft × 4 ft = 32 sq ft
32 sq ft × 12 in = 32 cu ft ÷ 27 = 1.19 cu yd
Topsoil: 32 cu ft × ⅔ = 21.33 cu ft
Compost: 32 cu ft × ⅓ = 10.67 cu ft
21.33 cu ft ÷ 0.75 cu ft a bag = 29 bags of topsoil
10.67 cu ft ÷ 1 cu ft a bag = 11 bags of compost
Bags or a delivered load
A cubic yard is 27 cubic feet, so bags add up quickly. Soil is sold by the cubic yard and can be ordered as a topsoil and compost blend, which usually makes a delivered load the cheaper way to fill several beds. For one or two small beds, bags are easier to handle: at the typical $9.98 for a 1.5 cu ft bag of raised bed soil, a 4 × 8 ft bed 12 in deep costs about $220 in bags.
| Bag size | Bags in a cubic yard | Bags for a 4 × 8 ft bed, 12 in deep |
|---|---|---|
| 0.75 cu ft | 36 | 43 |
| 1 cu ft | 27 | 32 |
| 1.5 cu ft | 18 | 22 |
| 2 cu ft | 14 | 16 |
| Item | Typical | Range | Stores |
|---|---|---|---|
| 1.5 cu ft bag of raised bed soil | $9.98 | $7.19 to $12.99 | 9 |
| 0.75 cu ft bag of topsoil | $2.97 | $2.58 to $3.37 | 5 |
| 1 cu ft bag of compost | $9.49 | $3.99 to $21.00 | 12 |
| 2 cu ft bag of potting mix | $12.99 | $8.35 to $19.97 | 7 |
Soil for pots and planters
For a round planter, choose "Round bed or planter" and enter its width across the top and the depth of soil. Potting mix is often sold by the dry quart; a cubic foot is about 25.7 dry quarts, so an 8 qt bag holds roughly a third of a cubic foot. These are the volumes of a few common pot sizes, treating each as a straight-sided cylinder, which slightly overstates a tapered pot:
| Pot | Volume | Potting mix |
|---|---|---|
| 10 in round pot, 9 in deep | 0.41 cu ft | 11 dry qt |
| 12 in round pot, 11 in deep | 0.72 cu ft | 19 dry qt |
| 16 in round pot, 14 in deep | 1.63 cu ft | 42 dry qt |
| 20 in round pot, 17 in deep | 3.09 cu ft | 79 dry qt |
Sources
- Building a Raised Bed Garden (E-560), Texas AgriLife Extension Service, Texas A&M System (Files, Arnold, Welsh and Dainello), March 2009. Eight to 12 in deep is usually adequate, vegetable beds 12 to 18 in; soil is sold by the cubic yard and can be ordered as a topsoil and compost blend; common blends ¾ topsoil and ¼ compost, ⅔ and ⅓, or half and half; for vegetables, a third each of topsoil, peat moss and sand or coarse perlite; potting soil is good but usually too expensive for large beds.
- Soil to Fill Raised Beds, University of Maryland Extension (Jon Traunfeld; reviewed by Neith Little), updated 6 November 2024. Over existing soil, compost and purchased topsoil in a 1:2 or 1:1 ratio; on a hard surface, compost and a soilless growing mix 1:1, at least 8 in deep for leafy greens, beans and cucumbers and 12 to 24 in for peppers, tomatoes and squash; topsoil up to 20% by volume in beds at least 16 in deep; bagged "organic soil" typically contains no topsoil.
- How Much Compost, Soil or Mulch Do I Need to Purchase?, Texas AgriLife Extension Service, Travis County, February 2010. Square feet times depth in inches, divided by 324, gives cubic yards.
- Online store listings for bagged concrete, mortar, grout, block, rebar, mesh, gravel, sand, soil, mulch and pavers, Google Shopping results (Home Depot, Lowe's, Menards, Ace Hardware, Walmart and others), November 2026. Single-item prices by store; the calculators use the median as the default and show the range.