How to measure for your raised bed soil project
- Measure your bed interior. Measure the inside length and inside width of the frame in feet. If you have a non-rectangular bed (keyhole, octagon), measure the longest span as length and the widest span as width — the result will be a slight overestimate, which is fine.
- Choose a fill depth. Enter how deep you plan to fill in inches. Use 6–8 inches for shallow-rooted crops like lettuce and herbs, 10–12 inches for tomatoes, peppers, and squash, and 12–18 inches for carrots, parsnips, or other deep-rooted crops. If you're filling a very deep bed cheaply, see the hügelkultur tip below.
- Add the number of beds. If all your beds are the same size, enter the count and the calculator multiplies for you. For beds of different sizes, run the calculator once per bed and add the totals. Then check the bag vs. bulk tip — above about 1 cubic yard, a bulk delivery usually saves money.
How the raised bed soil calculator works
The volume of a rectangular raised bed is simply length × width × depth, all in the same units. Because depth is entered in inches, we first divide by 12 to convert to feet, then multiply all three dimensions to get cubic feet. For a 4 × 8 ft bed at 12 inches deep: 4 × 8 × (12 ÷ 12) = 4 × 8 × 1 = 32 cubic feet. To find cubic yards, divide by 27: 32 ÷ 27 ≈ 1.19 cubic yards. For bags, divide the cubic feet by the bag size and round up to the nearest whole bag: 32 ÷ 2 = 16 of the 2 cu ft bags, and ⌈32 ÷ 1.5⌉ = 22 of the 1.5 cu ft bags. Multiple beds multiply linearly — two 4×8 beds at 12 inches needs 64 cu ft, 32 of the 2 cu ft bags.
Which type are you estimating?
Mel's Mix (square-foot gardening)
The classic blend from Mel Bartholomew's All New Square Foot Gardening: one third compost, one third peat moss or coir, one third coarse vermiculite. It drains well, never compacts, and needs no native soil at all. It costs more per cubic foot than topsoil blends, so it's most economical in shallower beds (6–8 inches) or smaller 4×4 frames.
Enter: Enter your bed dimensions with 6–8 in depth; buy compost, coir, and vermiculite in equal volumes
Topsoil + compost blend (budget fill)
A common budget approach: fill the bottom two-thirds with quality topsoil or screened garden soil and top off with an inch or two of compost each season. A roughly 60/40 split of topsoil to compost gives good structure and drainage at a lower cost than all-bagged mixes. Works especially well for larger or deeper beds where pure Mel's Mix would be expensive.
Enter: Enter full depth; plan roughly 60% topsoil + 40% compost by volume
Bagged raised-bed / garden soil (convenience)
Pre-blended bagged raised-bed soil is the most convenient option — available at any garden center, labeled for in-ground or raised-bed use. It's more expensive per cubic foot than buying topsoil and compost separately, but requires no mixing. Best for small fills (under 1 cubic yard) where the premium is worth the time saved.
Enter: Enter your depth; the 2 cu ft bag count is shown directly — pick up that many bags
Shallow fill for greens and herbs (6–8 in)
Lettuce, spinach, kale, basil, cilantro, and most herbs have short roots and thrive in just 6–8 inches of good soil. A 4×8 bed at 6 inches needs only 16 cu ft (8 of the 2 cu ft bags). This is also the right depth if you're placing the bed over existing in-ground soil that the roots can extend into.
Enter: Enter 6 in depth for shallow-rooted crops — halves soil cost vs. a 12 in fill
Deep fill for tomatoes and root crops (12–18 in)
Tomatoes, peppers, squash, carrots, parsnips, and beets need 12–18 inches of unobstructed soil. For tall, deep beds, reduce cost by layering logs, branches, and wood chips at the bottom (hügelkultur) — they decompose over time and improve drainage. Fill the top 12–14 inches with your soil mix; that's where roots actively feed.
Enter: Enter 12–18 in depth; consider hügelkultur fill for the bottom 6–8 in of very deep boxes
Tips & ways to save
- Soil settles 10–20% after the first few waterings. Slightly overfill your bed or keep a bag or two in reserve to top up after the first season.
- Above about 1 cubic yard (27 cu ft, roughly 14 of the 2 cu ft bags), a bulk cubic-yard delivery from a landscape supplier is usually cheaper per cubic foot than buying bags. Call ahead — minimum orders and delivery fees vary.
- For deep beds on a budget, fill the bottom third with logs, branches, straw, or other organic matter (hügelkultur style). The wood breaks down slowly, improves drainage, and cuts how much purchased soil you need.
- Never use straight topsoil in a raised bed — it compacts quickly without good drainage. Always mix in compost (at least 25–30% by volume) or use a product labeled specifically for raised beds.
- For a very rough bags-to-volume check: take your cubic foot total, divide by 2 for the 2 cu ft bag count, or divide by 1.5 and round up for the 1.5 cu ft bag count. A 4×8 bed at 12 inches = 32 cu ft ÷ 2 = 16 bags.
Soil to fill one raised bed
| Bed size | Depth | Cubic feet | 1.5 cu ft bags | 2 cu ft bags |
|---|---|---|---|---|
| 4 × 4 ft | 6 in | 8 cu ft | 6 | 4 |
| 4 × 4 ft | 12 in | 16 cu ft | 11 | 8 |
| 4 × 4 ft | 18 in | 24 cu ft | 16 | 12 |
| 4 × 8 ft | 6 in | 16 cu ft | 11 | 8 |
| 4 × 8 ft | 12 in | 32 cu ft | 22 | 16 |
| 4 × 8 ft | 18 in | 48 cu ft | 32 | 24 |
One cubic yard (27 cu ft) fills about a 4×8 bed 10 inches deep and equals about 14 of the 2 cu ft bags. Soil settles, so slightly overfill or top up after the first watering.
Frequently asked questions
How much soil do I need for a 4×8 raised bed?
How many bags of soil fill a raised bed?
Is bagged or bulk soil cheaper for raised beds?
How deep should a raised bed be?
What is the best soil mix for a raised bed?
How do I fill a deep raised bed cheaply?
Sources
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Reviewed by the BackyardCalc editorial team. Figures are computed from the formula above and checked against manufacturer yields.