Raised Bed Soil Calculator: Cubic Feet & Bags
Calculate how much soil to fill one or several raised garden beds — in cubic feet, cubic yards and bags — and how to split it between topsoil, compost and aeration material.
A 4 × 8 ft raised bed filled 12 inches deep holds 32 cubic feet of soil, about 1.2 cubic yards or 22 bags of 1.5 cu ft. A common mix is 50% topsoil, 40% compost and 10% perlite or coarse sand for drainage.
Your numbers
Result
How much raised bed soil do you need?
A raised bed is a rectangular box, so its soil volume is length × width × depth. Multiply by the number of beds and convert to the unit you buy.
cubic yards = cubic feet ÷ 27
Soil needed for common raised bed sizes
| Bed size | 6 in deep | 12 in deep | Bags (1.5 cu ft, 12 in) |
|---|---|---|---|
| 3 × 3 ft | 5 cu ft | 9 cu ft | 6 |
| 4 × 4 ft | 8 cu ft | 16 cu ft | 11 |
| 3 × 6 ft | 9 cu ft | 18 cu ft | 12 |
| 4 × 6 ft | 12 cu ft | 24 cu ft | 16 |
| 4 × 8 ft | 16 cu ft | 32 cu ft | 22 |
| 4 × 10 ft | 20 cu ft | 40 cu ft | 27 |
| 4 × 12 ft | 24 cu ft | 48 cu ft | 32 |
A 4 × 8 foot bed filled 12 inches deep holds 32 cubic feet — about 1.2 cubic yards, or 22 bags of 1.5 cu ft.
What to fill it with
Plain topsoil is too dense for containers. A popular blend is roughly half screened topsoil, 40% compost and 10% perlite or coarse sand for drainage. Bulk soil blends labeled "raised bed mix" or "garden soil" are the cheapest way to fill several beds — use the topsoil calculator to compare bulk quantities.
Choosing a raised bed frame
| Material | Lifespan | Notes |
|---|---|---|
| Cedar or redwood | 10–15 years | Naturally rot-resistant; popular for vegetables |
| Pressure-treated lumber | 10–20 years | Modern ACQ/CA treatments are widely used for food gardens; many gardeners line the inside |
| Galvanized steel | 20+ years | Warms quickly, holds a lot of soil |
| Concrete block | Decades | Cores can hold herbs or flowers |
Keep beds no wider than 4 feet so you can reach the middle from either side without stepping on the soil, and leave 2–3 feet between beds for paths.
Save on soil
Filling the bottom third to half of tall beds with logs, branches and leaves (hügelkultur) cuts soil needs and feeds the bed as it breaks down. Tick the box above to see the reduced volume.
After planting, finish with 2 inches of mulch to hold moisture.
Frequently asked questions
How many bags of soil for a 4×8 raised bed?
A 4×8 bed filled 12 inches deep needs 32 cubic feet, which is about 22 bags of 1.5 cu ft soil.
How deep should a raised bed be?
Vegetables do well in 8–12 inches. Root crops like carrots and potatoes prefer 12 inches or more.
Is bulk soil cheaper than bags?
Almost always. A cubic yard of bulk garden soil costs about as much as 4–6 bags and fills 27 cubic feet instead of 6–9.
What's the best mix for raised beds?
A common recipe is 50% topsoil, 40% compost and 10% aeration material such as perlite, vermiculite or coarse sand.
How much soil for a 4×4 raised bed?
A 4×4 bed at 12 inches deep needs 16 cubic feet — about 11 bags of 1.5 cu ft or 0.6 cubic yards.
Can I put cardboard at the bottom of a raised bed?
Yes. Plain cardboard smothers grass and weeds and breaks down in a season; remove tape and labels first.
Do I need to refill a raised bed every year?
Top it up with compost each spring as the soil settles and nutrients are used.
How do I calculate soil for a round raised bed?
Use π × radius² × depth. A 4-ft-diameter bed at 12 inches deep needs 12.6 cubic feet.
Sources and further reading
- Soil to fill raised beds — University of Maryland Extension
- Growing vegetables in raised beds — University of Maryland Extension
These references support the general guidance on this page. The calculator applies the standard formulas shown above to the numbers you enter.
Related calculators
. Estimates only. Always confirm quantities with your supplier or a qualified contractor before ordering, and add extra for waste and site conditions.