Raised Bed Soil Calculator
Enter the bed's length, width and fill depth, how many beds, and the mix you want. You get cubic feet and yards, the bags or bulk delivery to buy with costs, and how much of each component the mix needs.
Fill depth, not bed height; leave 1-2 in. of freeboard.
Soil needed
32.0 cu ft
1.19 cu yd
In bags
22 × 1.5 cu ft
$176 at $8/bag
In bulk
1.5 cu yd
$68 at $45/yd + delivery
Bulk wins above
~1 cu yd
27 bags of 1 cu ft vs one delivery
60 / 30 / 10: what to buy
| Component | Share | Cubic feet | 1.5 cu ft bags |
|---|---|---|---|
| Topsoil | 60% | 19.2 | 13 |
| Compost | 30% | 9.6 | 7 |
| Perlite, bark fines or coarse sand | 10% | 3.2 | 3 |
8 × 4 × (12 ÷ 12) = 32.0 cu ft per bed; ÷ 27 for yards. Soil settles 10-20% in the first season; overfill a little or plan to top up.
Cubic feet of soil by bed size and depth
| Bed (ft) | 6 in. | 8 in. | 10 in. | 12 in. | 18 in. | 24 in. |
|---|---|---|---|---|---|---|
| 4 × 4 | 8.0 (0.30 yd) | 10.7 (0.40 yd) | 13.3 (0.49 yd) | 16.0 (0.59 yd) | 24.0 (0.89 yd) | 32.0 (1.19 yd) |
| 4 × 8 | 16.0 (0.59 yd) | 21.3 (0.79 yd) | 26.7 (0.99 yd) | 32.0 (1.19 yd) | 48.0 (1.78 yd) | 64.0 (2.37 yd) |
| 4 × 12 | 24.0 (0.89 yd) | 32.0 (1.19 yd) | 40.0 (1.48 yd) | 48.0 (1.78 yd) | 72.0 (2.67 yd) | 96.0 (3.56 yd) |
| 3 × 6 | 9.0 (0.33 yd) | 12.0 (0.44 yd) | 15.0 (0.56 yd) | 18.0 (0.67 yd) | 27.0 (1.00 yd) | 36.0 (1.33 yd) |
| 2 × 8 | 8.0 (0.30 yd) | 10.7 (0.40 yd) | 13.3 (0.49 yd) | 16.0 (0.59 yd) | 24.0 (0.89 yd) | 32.0 (1.19 yd) |
| 4 × 16 | 32.0 (1.19 yd) | 42.7 (1.58 yd) | 53.3 (1.98 yd) | 64.0 (2.37 yd) | 96.0 (3.56 yd) | 128.0 (4.74 yd) |
Bags per cubic yard, and when bulk wins
| Bag size | Bags per cu yd | Cost per yd at $6/bag | at $10/bag |
|---|---|---|---|
| 0.75 cu ft | 36 | $216 | $360 |
| 1 cu ft | 27 | $162 | $270 |
| 1.5 cu ft | 18 | $108 | $180 |
| 2 cu ft | 14 | $84 | $140 |
| 3 cu ft | 9 | $54 | $90 |
Bulk garden mix is typically $35 to $70 a yard plus $50 to $100 delivery, so one yard is the break-even and two is a clear win.
The mixes
| Mix | Recipe | Best for |
|---|---|---|
| Square-foot mix (Mel's mix) | 33% compost (blended), 33% peat moss or coir, 33% coarse vermiculite | Shallow (6-8 in.) intensive beds; light and expensive |
| 60 / 30 / 10 | 60% topsoil, 30% compost, 10% perlite, bark fines or coarse sand | Deep beds; cheapest per yard, holds water well |
| 50 / 50 topsoil and compost | 50% topsoil, 50% compost | Simple and cheap; add perlite if it compacts |
| Bagged raised-bed mix | 100% raised bed mix | Small beds and containers; convenience |
Frequently Asked Questions
How much soil do I need for a 4 × 8 raised bed?
Length × width × depth in feet. A 4 × 8 bed filled 12 inches deep is 32 cubic feet, about 1.19 cubic yards: 22 bags of 1.5 cu ft or 16 bags of 2 cu ft. At 10 inches it is 26.7 cu ft; at 18 inches 48.
How many bags of soil is a cubic yard?
27 cubic feet: 27 one-cubic-foot bags, 18 of 1.5 cu ft, or 13.5 of 2 cu ft. Bagged soil runs $5 to $12 a bag, so a yard in bags is $150 to $250 against $30 to $60 bulk plus delivery. Bulk wins from about one yard up, if you can take a pile on the driveway.
What mix should I fill a raised bed with?
Not bagged topsoil alone (it compacts) and not pure compost (it slumps and gets too rich). The common recipes: Mel's square-foot mix of equal parts compost, peat or coir, and coarse vermiculite for shallow beds; or 60% topsoil, 30% compost, 10% aeration (perlite, bark fines or coarse sand) for deep beds -- cheaper and heavier. Bagged 'raised bed mix' is roughly the second recipe ready-made.
Do I need to fill the whole depth with good soil?
For beds over 18 inches, no. Fill the bottom third with logs, branches, straw or coarse wood chips (the hugelkultur approach), then the mix on top. Roots of most vegetables live in the top 12 inches. Expect the fill to settle 10-20% in the first year; top up with compost.
These calculators use published seeding rates, extension-service fertilizer guidance, and standard pool-chemistry dosing figures, and are for planning. Read the product label; it governs the dose. Pool chemicals are hazardous when mixed or mishandled, and a pool store's water test beats any estimate here.