Get exact cubic feet, cubic yards, bag counts, and component breakdown for any raised bed mix.
The soil you fill a raised bed with is one of the most consequential decisions in your entire garden setup. Unlike in-ground beds where years of amendment gradually improve native soil, raised beds live or die almost entirely on the quality of their initial fill. Native soil is almost never the right choice — it compacts under watering, drains poorly in clay-heavy regions, and lacks the organic matter and biological activity that vegetables need to thrive. Most experienced raised bed gardeners choose between three approaches: Mel's Mix (the classic square foot gardening blend), a topsoil-plus-compost 50/50 blend, or a purchased "raised bed mix" from a landscape supplier that is similar in composition to Mel's Mix but pre-blended.
The calculator above helps you determine exactly how many cubic feet of material you need based on bed dimensions and depth, and breaks down component quantities for the mix type you select. Knowing your numbers before you shop saves significant money — buying twice as many bags as needed or discovering you're short on fill after the lumber is already built are both common and avoidable mistakes.
Mel's Mix — one-third compost, one-third peat moss or coco coir, and one-third coarse vermiculite — was developed by Mel Bartholomew specifically for raised bed vegetable gardening. Its primary advantages are that it never compacts, drains exceptionally well, retains moisture between waterings through the peat or coir component, and is extremely lightweight compared to soil-based mixes. The drawback is cost: vermiculite is expensive, and filling a large 4x8x12" bed with pure Mel's Mix can cost $150–$250 in materials. The 50/50 topsoil-compost blend is significantly cheaper (especially when purchased in bulk by the yard), works well for most vegetables, but tends to compact somewhat over time and requires annual compost top-dressing to maintain structure.
Depth depends entirely on what you plan to grow. For shallow-rooted crops — lettuce, spinach, herbs, and most annual flowers — 6 inches of quality soil mix is sufficient. For most vegetables including tomatoes, peppers, beans, and brassicas, 12 inches is the standard recommendation and produces excellent results. Root vegetables are the most demanding: carrots, parsnips, and beets need at least 12 inches of loose, rock-free soil to develop properly, and longer carrot varieties like Imperator types need 14–18 inches. If your bed sits on compacted clay and you want deep root penetration, consider loosening the native soil beneath the bed with a broadfork before filling, which lets deep-rooted crops extend below the raised bed floor without the expense of filling the extra depth with expensive mix.
For intensive vegetable production, Mel's Mix (1/3 compost, 1/3 peat moss or coco coir, 1/3 coarse vermiculite) is the top performer in nearly every controlled comparison. It produces excellent drainage, aeration, and moisture retention simultaneously — qualities that are normally in tension with each other. For gardeners on a budget, a 50/50 blend of good quality topsoil and compost is the best value and grows excellent vegetables, though it requires annual compost additions to maintain structure. Avoid any mix labeled "garden soil" for use in raised beds — these mixes are designed to be tilled into native soil and become dense and waterlogged when used as the sole fill in a raised bed. Look for mixes specifically labeled "raised bed mix" or build your own from components.
Cost varies significantly by region and purchasing method. Bagged materials from big-box stores typically run $6–$12 per 1.5–2 cubic foot bag, making a 4x8x12" bed (32 cubic feet) cost $120–$250 in bags. Bulk landscape delivery becomes cost-competitive at roughly 4+ cubic yards (about 108 cubic feet) and can cut per-cubic-foot cost in half or more. A 50/50 topsoil-compost blend delivered in bulk averages $35–$60 per cubic yard depending on region. Mel's Mix built from bulk-purchased components (buying peat in large bales and vermiculite in 4 cubic foot bags) costs roughly $80–$120 per cubic yard versus $150–$200 from bagged retail, making it worth the extra sourcing effort for larger projects.
Cardboard (overlapped by 4–6 inches at seams) is an excellent option under raised beds placed on grass or weed-heavy ground. It smothers existing vegetation, decomposes within one season to allow earthworm access from below, and costs nothing. Avoid using black plastic weed barriers under raised beds — they block beneficial earthworm migration from native soil into the bed, can restrict drainage in heavy rain events, and do not decompose, meaning they become a persistent nuisance to remove years later. Hardware cloth (1/4" mesh galvanized steel) stapled to the underside of the bed frame is worth the expense if you have gophers or voles — they will tunnel up through the soil and decimate root crops within one season.
Native soil in a raised bed is almost always a mistake, with one limited exception: if your native soil is exceptionally sandy loam with good drainage and reasonable organic matter content (dark in color, not clay-heavy), you can blend it 50/50 with compost and get acceptable results at low cost. However, clay-heavy soil, which is the norm across much of the Midwest and Southeast, should never be used as raised bed fill. Clay compacts severely under watering, drains so slowly that roots suffocate in wet weather, and bakes to a concrete-like hardness in dry periods. Even modest amounts of clay mixed into a bed will noticeably degrade performance. If you have good native topsoil available, the most practical approach is to use it as a base for the bottom half of a deep bed and fill the top 8–10 inches with quality mix where roots do most of their work.
Raised bed soil loses volume each year as the organic matter in it oxidizes and is consumed by soil life — typically 10–20% annually in active, well-watered beds. The most important maintenance practice is top-dressing with 1–2 inches of finished compost each spring before planting. This replaces lost volume, replenishes nutrients, and re-inoculates the bed with beneficial microbial life. Avoid compacting raised beds by walking in them — this is why the standard 4-foot maximum width exists, so you can reach the center from both sides. Every 2–3 years, assess whether the soil needs a vermiculite or perlite boost to restore drainage if it has become dense. Beds managed with annual compost additions and no compaction can remain highly productive for a decade or more without a complete soil replacement.