Raised bed soil calculator
Enter your bed's footprint and depth — and how many beds you're filling — to get total soil volume, a Mel's Mix shopping list and 2 ft³ bag counts.
Result
Bed soil needed
How much soil do I need for a raised bed?
Bed volume is simply footprint × soil depth:
Formula
ft³ = length × width × depth (in) ÷ 12 · × number of beds
Classic example: a 4 ft × 8 ft bed filled to 12 inches holds 4 × 8 × 1 = 32 ft³ ≈ 1.2 yd³ — sixteen 2 ft³ bags, or about $45–60 of bulk blended soil.
| Bed size | 6 in deep | 12 in deep |
|---|---|---|
| 4 × 4 ft | 8 ft³ (4 bags) | 16 ft³ (8 bags) |
| 4 × 8 ft | 16 ft³ (8 bags) | 32 ft³ (16 bags) |
| 4 × 12 ft | 24 ft³ (12 bags) | 48 ft³ (24 bags) |
Mel's Mix vs budget fills
Mel Bartholomew's Square Foot Gardening recipe — equal parts compost, peat moss and vermiculite — is light, holds water and is weed-free, but it's the premium option. Cheaper layered approaches work well in deeper beds:
- Hügelkultur bottom: logs and branches (first ⅓–½ of tall beds), then leaves/grass, then 8–12 in of real soil on top.
- Budget blend: 50% topsoil + 30% compost + 20% aeration (perlite/aged bark). About half the cost of Mel's Mix.
- Never fill beds with 100% compost (compacts, too hot) or 100% fill dirt (roots stall).
Full recipes and costs: raised bed soil mix guide.
Depth by crop
- 6 inches: lettuce, herbs, radishes, strawberries.
- 12 inches: the practical default — tomatoes, peppers, beans, most flowers.
- 18+ inches: carrots/parsnips, potatoes, and better drainage in wet climates.
Frequently asked questions
How much soil for a 4×8 raised bed?
At 12 inches: 32 ft³ = 1.19 yd³ = sixteen 2 ft³ bags. At 6 inches it's exactly half that.
How many bags of soil do I need for my bed?
Take the bed's cubic feet and divide by the bag size (usually 2 ft³ for raised-bed soil, 1.5 ft³ for some brands). A 4×8×1 ft bed needs 16 of the 2 ft³ bags.
What is Mel's Mix?
Equal volumes of compost, peat moss (or coco coir) and coarse vermiculite. The calculator breaks your bed volume into those thirds automatically. Price per bed is highest, but it's the lightest and best-draining option.
Can I fill the bottom of a deep bed with cheaper material?
Yes — and you should. Logs, branches, leaves and even fill dirt can fill the bottom half of beds 18 in+ deep; keep the top 8–12 in for real growing mix.
How many cubic yards is 5 beds of 4×8 at 10 inches?
Each bed: 4 × 8 × 10/12 = 26.7 ft³; five beds = 133 ft³ = 4.9 yd³ — order 5 yards bulk and save a bundle over 67 bags.