How to calculate raised bed soil volume
Volume is the space inside the bed: its footprint multiplied by how deep you’ll fill it. Measure inside the frame, and use the same unit for every side.
How deep should a raised garden bed be?
Frame height and growing depth aren’t always the same. A bed can be tall for comfort or drainage while the plants only need part of that depth, and some beds sit on soil that roots can grow into. University of Georgia Extension advises that most garden crops need at least 10 inches of soil, and that a shallower bed should have the ground beneath it tilled so roots can continue down2; root crops such as potatoes want more. The right growing-medium depth still depends on what you grow and your site, so there’s no single number for every crop. Enter the depth you plan to fill; if that’s less than the frame height, use that depth rather than the frame height.
How many soil bags do I need?
| Bed size | Cubic feet | Cubic yards | 2 cu ft bags | 1.5 cu ft bags |
|---|---|---|---|---|
| 2 × 4 ft, 12 in deep | 8 | 0.30 | 4 | 6 |
| 4 × 4 ft, 12 in deep | 16 | 0.59 | 8 | 11 |
| 3 × 6 ft, 12 in deep | 18 | 0.67 | 9 | 12 |
| 4 × 8 ft, 12 in deep | 32 | 1.19 | 16 | 22 |
| 2 × 6 ft, 24 in deep | 24 | 0.89 | 12 | 16 |
| 4 × 8 ft, 18 in deep | 48 | 1.78 | 24 | 32 |
Bags rounded up to whole bags. No extra included for settling. Bagged raised-bed and garden soils are commonly sold in 1.5 and 2 cubic foot bags45; check the bag you’re buying.
Should I buy bagged or bulk soil?
It depends on quantity, local prices and access. Bags are easy to carry, store and buy in exact amounts, and suit small beds. Bulk soil is sold by the cubic yard (or cubic meter) and can work out cheaper for larger volumes, but delivery fees, minimum orders and where the pile can be dropped all matter. Bulk isn’t always cheaper. Enter the prices you’ve been quoted in the comparison above to see which comes out lower for your beds.
Can I fill the bottom of a tall raised bed with other materials?
Some gardeners put another material in the lower part of a tall bed to reduce how much growing mix they buy. Whether that suits your bed depends on the material, what you grow and how deep the roots need to go. Woody materials such as logs and branches can settle and decompose over time, so the surface may sink and need topping up. Use layered filling above to see the quantities for a depth you choose.
Frequently asked questions
How much soil for a 4 × 8 raised bed?
At 12 inches deep, a 4 × 8 ft bed holds 32 cubic feet: about 1.19 cubic yards, 16 bags of 2 cu ft or 22 bags of 1.5 cu ft. At 18 inches deep it holds 48 cubic feet.
How many bags of soil fill a 2 × 4 bed?
At 12 inches deep, a 2 × 4 ft bed holds 8 cubic feet: 4 bags of 2 cu ft or 6 bags of 1.5 cu ft. At 6 inches deep it’s 4 cubic feet: 2 bags of 2 cu ft or 3 bags of 1.5 cu ft.
How many cubic feet are in a cubic yard?
There are 27 cubic feet in a cubic yard, because a cubic yard is 3 ft × 3 ft × 3 ft.1
Do I need to fill a raised bed all the way to the top?
Not necessarily. Many gardeners leave a little room below the rim, which can make watering and mulching easier. This calculator measures to the depth you enter, so enter the depth you plan to fill.
Should I account for soil settling?
Often, yes. Soil and compost settle after filling and watering; University of Illinois Extension calls settling a fact of raised bed gardening and recommends top-dressing with a few inches of compost or topsoil each year.3 How much a bed settles varies by product and how loosely it was poured, so CalcBrite doesn’t assume a number. Use “Extra to buy” in the cost section to add a margin you choose.
Assumptions
- Volumes use the full depth you enter, measured inside the frame. Round beds use π × r² × depth.
- Unit conversions are exact definitions: 1 cu yd = 27 cu ft; 1 cu ft = 28.3168 L; 1 in = 2.54 cm.1
- Bag counts are rounded up to whole bags. Nothing is added for settling unless you choose an extra amount.
- Bag sizes offered (1.5 and 2 cu ft; 40 and 50 L) are common retail sizes, not a standard. Use “Custom” for any other bag.
- Prices are only what you enter. CalcBrite doesn’t store or estimate local soil prices.
- The calculator doesn’t recommend a growing depth, a lower-fill material or a ratio; the depth guidance above is cited from extension sources and your crop and site decide.
Sources
- Guide to the SI, Appendix B.8: cubic yard, cubic foot and short ton factors, NIST Special Publication 811.
- Raised Garden Bed Dimensions (Circular 1027-4), University of Georgia Cooperative Extension; Ballard, Berle & Westerfield; reviewed December 14, 2022 — “Most garden crops need at least 10 inches of soil to thrive”; shallower beds should have the soil beneath tilled.
- Refreshing raised bed soil generates exceptional results, University of Illinois Extension; Chris Enroth; April 5, 2021 — settling is “simply a fact of raised bed gardening”; top-dress annually with a few inches of compost or topsoil.
- Miracle-Gro Organic Raised Bed & Garden Soil, 1.5 cu. ft., Scotts Miracle-Gro (manufacturer product page) — example of the 1.5 cu ft bag size; “2 bags will fill a 2 ft. x 2 ft. x 6 in. raised bed garden” (manufacturer listing).
- Miracle-Gro Garden Soil All-Purpose, 2 cu. ft., Scotts Miracle-Gro (manufacturer product page) — example of the 2 cu ft bag size (manufacturer listing).
- Last reviewed:
- October 2026
- Last updated:
- October 9, 2026
- Calculator version:
- 1.0