Calculate exact cubic feet, cubic yards, and retail bags required for rectangular, round, L-shaped, and U-shaped raised garden beds. Features Mel's Mix recipe proportions, settling buffers, and Hugelkultur cost savings.
10%–15% for natural watering settling
Fills bottom with rotting logs, tree limbs, and leaves; tops with 12″ of premium soil.
Filling a raised bed flush with the top rim without accounting for settling leaves beds 3 to 5 inches below the top edge after the first deep watering. Our tool automatically incorporates an agronomic 10–15% compaction buffer so beds remain filled to optimal root depth.
Guessing bulk soil yardage leads to either mid-project shortages or massive surplus piles stranded on driveways that wash into gutters during rains. We convert exact interior cubic dimensions into exact commercial cubic yards and standard retail bag counts.
Filling raised beds with garden topsoil excavated from the yard leads to severe compaction, brick-like crusting, poor aeration, and stunted root systems. Our blend calculators formulate well-aerated potting mixes like Mel's Mix (peat/perlite/compost) for maximum root expansion.
Filling deep 24-inch or 30-inch corrugated metal beds entirely with premium soil mix costs hundreds of dollars unnecessarily. Our Hugelkultur layering feature models log, branch, and rough compost sub-bases to dramatically reduce the volume of purchased soil needed.
Accurate volumetric engines for rectangular lumber frames, galvanized stock tanks, circular rings, and oval beds.
Calculates exact components for Square Foot Gardening (1:1:1 compost, peat moss, coarse vermiculite) or custom blends.
Models bottom woody biomass fill in deep beds to save money and create a moisture-retaining sponge.
Compares delivered bulk scoops against 1.0, 1.5, and 2.0 cu ft retail store bags with price comparisons.
Choose Rectangular (standard 4x8 ft lumber), Circular, or Oval, and enter the total number of identical beds.
Measure inside the bed frame: enter length, width, and depth (leave 1–2 inches of top clearance for mulch).
Choose Mel's Mix (equal parts peat, vermiculite, compost), 60/40 Topsoil/Compost, or custom component ratios.
If your bed is deeper than 16 inches, specify bottom layer depth to fill with logs, sticks, leaves, and straw.
Keep the recommended 10–12% settling cushion so your soil level does not drop below root line after watering.
Instantly see total cubic yards for bulk delivery, counts for 1.5 and 2.0 cu ft retail bags, and component breakdowns.
Calculating raised bed soil requires finding inside frame cubic feet, converting to commercial cubic yards, and adding a compaction buffer:
Where \(L\) is inside length, \(W\) is width, \(D\) is depth in inches, and \(C\%\) is settling compaction buffer (typically 12%).
Divide \(V_{\text{cu ft}}\) by 27 to calculate commercial cubic yards for bulk ordering.
Engineered for Square Foot Gardening by Mel Bartholomew, Mel's Mix completely replaces heavy ground soil with three equal components by volume:
Never use a single compost variety. Blend 3 to 5 types: worm castings, mushroom compost, cow manure, and leaf mold for complete biological nutrition.
Holds up to 20 times its weight in water, releasing moisture gradually to plant root hairs during scorching summer heat waves.
Permanent expanded mineral that prevents soil from ever compacting. Retains dissolved nutrients via high Cation Exchange Capacity.
Modern corrugated metal beds stand 24 to 32 inches tall for ergonomic comfort. Filling a 30-inch tall bed completely with store-bought soil is an unnecessary waste of money:
| Retail Bag Size | Volume (Cu Ft) | Dry US Quarts | Metric Liters | Bags per Cu Yard |
|---|---|---|---|---|
| 0.75 cu ft Bag | 0.75 cu ft | 19.3 qt | 21.2 L | 36 bags |
| 1.0 cu ft Bag | 1.00 cu ft | 25.7 qt | 28.3 L | 27 bags |
| 1.5 cu ft Bag | 1.50 cu ft | 38.6 qt | 42.5 L | 18 bags |
| 2.0 cu ft Bag | 2.00 cu ft | 51.4 qt | 56.6 L | 13.5 bags |
Ordering bulk soil from a local landscape supply yard becomes significantly cheaper once your project requires more than 1.5 to 2.0 cubic yards (approx. 27 to 36 bags). Bagged retail soil averages $8.00 to $12.00 per 1.5-cu-ft bag ($144 to $216 per cu yd). Bulk custom garden soil blends cost $40 to $65 per cubic yard plus a $50 to $75 delivery fee, delivering dramatic cost savings for multi-bed setups.
Freshly shoveled soil contains substantial trapped air voids and naturally settles by 10% to 15% after the first 2 to 3 thorough waterings. If you fill a 12-inch bed flush to the top rim without adding a settling buffer, it will slump down to 10.5 inches, exposing bare frame walls to the sun. Always add a 12% compaction buffer so your beds finish at true target depth.
Lay 2 to 3 layers of plain corrugated cardboard directly over existing turf. It smothers weeds and grass, then naturally decomposes within 4 to 6 months into rich worm food.
If your region has burrowing gophers, voles, or moles, staple 1/2-inch galvanized wire mesh across the entire bottom frame to prevent rodents from tunneling up into vegetable roots.
| Bed Depth | Vegetables Supported | Root System Architecture |
|---|---|---|
| 6 to 8 Inches | Lettuce, spinach, radishes, strawberries, shallow herbs | Fibrous, shallow root spread |
| 10 to 12 Inches (Standard) | Tomatoes, peppers, cucumbers, bush beans, broccoli, kale, carrots | Deep lateral roots and moderate taproots |
| 18+ Inches (Deep) | Sweet potatoes, asparagus, melons, winter squash, pumpkins | Expansive anchor taproots and high water reservoir needs |
Never dig out or discard old raised bed soil. Because organic matter decomposes, bed levels drop 1 to 2 inches every growing season. In early spring, top-dress the bed with 1 to 2 inches of freshly screened organic compost or composted worm castings, and gently loosen with a broadfork to restore microbial life and aeration.
Expert answers on raised bed soil calculations, Mel's Mix, retail bags, and Hugelkultur methods.
