Your Result Explained: Exact Takeoff Breakdown
Many patio and urban gardeners prefer a pair of 4 ft × 4 ft square raised beds over a single 4×8 bed because you can walk all four sides and rotate crops cleanly between the two squares. A single 4×4 bed covers 16 square feet; filled to 10 inches deep (inside a 12-inch frame), one bed requires 13.33 cubic feet of soil.
Doubling that for two 4×4 beds gives 26.67 cubic feet—which is 0.99 cubic yards (practically 1 exact cubic yard). In retail bags, 26.67 cubic feet takes 18 bags of 1.5-cubic-foot raised bed soil (9 bags per bed) or 14 bags of 2.0-cubic-foot potting mix (7 bags per bed).
Eighteen bags of 1.5 cu ft soil weighs roughly 630 to 720 lbs total, making it easy to pick up in a single SUV or crossover trip.
Worked Math: Single vs. Pair of 4 ft × 4 ft Beds at 10 Inches
Computing volume and retail bag count for one and two 4×4 square garden beds filled 10 inches deep.
- Single 4×4 Bed Area = 4 ft × 4 ft = 16 sq ft.
- Depth in Feet = 10 in ÷ 12 = 0.8333 ft.
- Single Bed Volume = 16 sq ft × 0.8333 ft = 13.33 cubic feet (9 bags of 1.5 cu ft).
- Two 4×4 Beds Total Volume = 13.33 × 2 = 26.67 cubic feet (0.99 cubic yards).
- Total 1.5 cu ft Bags = Ceiling(26.67 ÷ 1.5) = 18 bags (9 bags per bed).
- Total 2.0 cu ft Bags = Ceiling(26.67 ÷ 2.0) = 14 bags (7 bags per bed).
Bottom Line: Buy 9 bags of 1.5 cu ft soil for one 4×4 bed at 10 inches deep, or 18 bags (or 1 bulk cubic yard) for two 4×4 beds.
How This Scenario Is Calculated
Two 4×4 beds have the exact same combined surface area (16 + 16 = 32 sq ft) as one 4×8 bed, so the soil volume at any given depth is identical.
If you fill your two 4×4 beds to the full 12-inch rim instead of 10 inches, total volume increases from 26.67 cu ft to 32.00 cu ft (22 bags of 1.5 cu ft soil, or 11 bags per bed).
Cubic Feet = Area (sq ft) × (Fill Depth in inches ÷ 12) × Number of Beds × (1 + Waste%) Cubic Yards = Cubic Feet ÷ 27 | Bags = Ceiling(Cubic Feet ÷ Bag Size) Project-Specific Tips & Common Mistakes
Dedicate One 4×4 Bed to Solanums and One to Brassicas/Greens
Having two separate 4×4 soil boxes makes annual crop rotation effortless: plant tomatoes and peppers in Bed A while growing kale, broccoli, and bush beans in Bed B, then swap next year.
Add a 16-Square Grid Frame for True Square Foot Spacing
Snap 1-foot grid lath strips across the top of each 4×4 box to divide it into sixteen 1×1 ft planting squares.
Mistake Placing two 4x4 beds less than 24 inches apart
Recommended Fix: Leave at least 30 to 36 inches of pathway between raised beds so a standard wheelbarrow and kneeling pad can pass through comfortably.
Reference Coverage Table (Lightweight Raised Bed / Soilless Potting Mix (Peat/Coir, Compost, Perlite))
Compare how coverage changes across common depths for Lightweight Raised Bed / Soilless Potting Mix (Peat/Coir, Compost, Perlite) (default planning density 900 lbs/yd³):
| Depth | 1 Cubic Yard Covers | 1 Ton Covers | Yards / 100 sq ft | Tons / 100 sq ft | Bags (1.5 ft³) / 100 sq ft |
|---|---|---|---|---|---|
| 6 in | 54 sq ft | 120 sq ft | 1.85 yd³ | 0.83 tons | 34 bags |
| 8 in | 40.5 sq ft | 90 sq ft | 2.47 yd³ | 1.11 tons | 45 bags |
| 10 in Active | 32.4 sq ft | 72 sq ft | 3.09 yd³ | 1.39 tons | 56 bags |
| 12 in | 27 sq ft | 60 sq ft | 3.7 yd³ | 1.67 tons | 67 bags |
| 18 in | 18 sq ft | 40 sq ft | 5.56 yd³ | 2.5 tons | 100 bags |
| 24 in | 13.5 sq ft | 30 sq ft | 7.41 yd³ | 3.33 tons | 134 bags |
Reference Source: Cornell Peat-Lite & Square Foot Gardening (1:1:1 Mel’s Mix) bulk density data.
Frequently Asked Questions
How many bags of soil for ONE 4x4 raised bed 12 inches deep?
One 4×4 bed at 12 inches deep holds 16 cubic feet, requiring 11 bags of 1.5-cubic-foot soil or 8 bags of 2.0-cubic-foot soil.
How many bags of soil for ONE 4x4 raised bed 6 inches deep?
One 4×4 bed at 6 inches deep holds 8 cubic feet, requiring 6 bags of 1.5-cubic-foot soil or 4 bags of 2.0-cubic-foot soil.
How many 0.75 cu ft topsoil + 1.0 cu ft compost bags do I need for a 4x4 bed?
For a 13.33 cu ft fill (10" deep), mix 9 bags of 0.75 cu ft topsoil (6.75 cu ft) with 7 bags of 1.0 cu ft compost (7.0 cu ft) for a total of 13.75 cubic feet.
Do two 4x4 beds use more lumber than one 4x8 bed?
Yes—two 4×4 beds have 32 linear feet of perimeter wall compared to 24 linear feet for a single 4×8 bed, requiring one extra 8-foot board per tier, but they use the exact same amount of soil.
Can I put 4x4 raised beds on a concrete patio?
Yes, provided the bed is at least 10 to 12 inches deep, lined with breathable landscape fabric to keep soil from washing out the bottom cracks, and filled with a lightweight soilless raised-bed mix.