How much soil for a raised garden bed? Bags vs. bulk

Two 4×8-foot raised beds, 11 inches deep, and you're standing in the garden center aisle doing math on your phone: do you fill your cart with bags, or call a landscape supplier for a bulk delivery? Grab too few bags and you're back at the store for a second trip with half-planted beds sitting empty. Order bulk for a small bed and you're paying a delivery minimum for three wheelbarrows' worth of soil. The right answer depends entirely on volume, and the crossover point comes sooner than most first-time bed builders expect.

Two ways to fill a raised bed

There are two common recipes for what actually goes in the bed, and they behave very differently on both cost and long-term performance.

Mel's Mix — the square-foot-gardening classic

Mel's Mix, popularized by Square Foot Gardening, is an equal-thirds blend: one-third compost, one-third peat moss or coconut coir, and one-third coarse vermiculite. No native soil at all. The appeal is real — it's light, drains well, resists compaction, and needs almost no tilling year to year because it never had garden soil's clay or subsoil problems to begin with. The tradeoff is cost: vermiculite in particular is priced more like a specialty amendment than a bulk fill, so Mel's Mix is usually the more expensive way to fill a bed, especially a deep one.

The simple blend — topsoil and compost

A more conventional and cheaper approach is roughly 60% topsoil to 40% compost. It behaves more like garden soil because it substantially is garden soil, amended for organic matter and drainage. It compacts more over seasons than Mel's Mix and benefits from an annual compost top-up, but it's dramatically cheaper to fill, especially at scale, because topsoil is one of the least expensive bulk materials a landscape yard sells.

Neither is objectively "correct" — Mel's Mix earns its cost in raised beds meant for intensive square-foot planting where drainage and low compaction matter most; the simple blend earns its keep in larger beds, in-ground-adjacent beds, or budget-conscious builds where a soil test and a yearly compost refresh do most of the work Mel's Mix does automatically.

Bags vs. bulk — where the crossover happens

Bagged soil is sold by the bag, typically in the 1–2 cubic foot range, at a price per bag. Bulk soil or compost is sold by the cubic yard (27 cubic feet), usually delivered by dump truck, often with a delivery minimum. The comparison that decides which is cheaper is straightforward: bags-needed × price-per-bag versus cubic-yards-needed × price-per-yard.

What surprises people is how quickly bulk wins. A single small bed might only need 5–6 cubic feet, well under a cubic yard, where a bulk delivery minimum makes bags the obvious and only sensible choice. But once total volume climbs into the 1+ cubic yard range — which two or three medium beds reach easily — bulk pricing per cubic foot is usually a fraction of bagged pricing per cubic foot, because you're not paying for individual plastic bags, pallet handling, and retail markup on each one.

• Small volume, one bed: bags almost always win — no delivery minimum, no leftover pile, buy exactly what you need.
• Several beds or one large bed: run the comparison — this is the zone where bulk usually overtakes bags.
• Large volume, multiple beds or a full garden build-out: bulk wins decisively, often at half the per-cubic-foot cost of bags or less.

Depth matters more than people assume

Volume is length × width × depth, and depth is the dimension people most often shortchange when estimating. An 11-inch-deep bed and a 6-inch-deep bed with the same footprint don't need "close to" the same soil — the 11-inch bed needs nearly double. Because most lumber-built raised beds use standard board widths (a single 2×12 gives roughly 11 inches, two stacked 2×6 boards give roughly 11 as well), it's worth converting your actual board height to inches and using that exact number rather than rounding to "about a foot," since that rounding compounds across every bed in a multi-bed layout.

Worked example: two 4×8 beds at 11 inches

Two beds, each 8 ft long, 4 ft wide, 11 inches deep, filled with Mel's Mix:

• Volume per bed: 8 ft × 4 ft × (11/12 ft) ≈ 29.33 cu ft
• Total volume, 2 beds: 29.33 × 2 ≈ 58.67 cu ft, or about 2.17 cu yd
• Bagged option, 1.5 cu ft bags at $10/bag: ceil(58.67 ÷ 1.5) = 40 bags, or $400
• Bulk option at $45/cu yd: 2.17 × $45 ≈ $97.78

Bulk wins by roughly $300 at this volume — a difference big enough that it's worth the delivery even though these are only two modest beds. Within that mix, the equal-thirds split works out to about 19.6 cu ft each of compost, peat moss or coir, and vermiculite. A single small 4×4×11" bed alone, by contrast, needs only about 14.7 cu ft — under a cubic yard — where the bagged option at 10 bags ($100) beats a bulk delivery minimum that a supplier might charge for such a small amount.

Run your own beds through the numbers

The crossover point between bags and bulk depends on your specific bed count, dimensions, and local pricing for both — there's no single "always do this" rule. Our raised garden bed soil calculator takes your bed dimensions and count, lets you pick Mel's Mix or the simple topsoil/compost blend, and returns the total volume, the bagged and bulk cost side by side, and the full ingredient breakdown — so you know which option is actually cheaper before you load the cart or call the yard.