Soil Calculator: Raised Garden Bed & Bulk Soil Estimator
Use this soil calculator to determine how much topsoil, garden blend, or compost is needed for raised garden beds, round planters, and lawn topdressing. Includes compaction settling allowances and bag size conversions.
Order 2.75 cubic yards of bulk garden soil mix delivered (saving considerable money over 47 individual bags).
| Number of Planter Beds / Pots | 2 identical beds |
|---|---|
| Soil Depth Filling Layer | 12 inches |
| Settling & Compaction Margin | 10% |
| Total Volume in Cubic Feet | 70.4 cu ft |
| Total Volume in Cubic Yards | 2.61 yd³ |
| Pre-Packaged Bags Required (1.5 cu ft) | 47 bags |
| Estimated Soil Weight (1 t/yd³) | 2.61 Tons (5,215 lbs) |
📐 Show Formula and Default Assumptions
We believe all home improvement estimates should be transparent and verifiable. Below is the exact math running in this browser tool:
-
Raised Bed Volume:
Cubic Feet = Length ft × Width ft × (Depth in ÷ 12)Calculates three-dimensional internal garden planter soil capacity. -
Soil Settling / Compaction:
Total Soil Needed = Base Volume × (1 + Settling% / 100)Fluffy organic topsoil and compost blends settle 10% to 15% after initial watering and planting. -
Bag Size Versatility:
Bags Needed = ceil( Total Volume cu ft ÷ Selected Bag Size cu ft )Supports standard 1.0 cu ft, 1.5 cu ft, and 2.0 cu ft soil packaging.
Note: All default assumptions (waste %, coverage rates, container yields) can be adjusted directly in the input fields above to match your project specifications.
How to Measure Raised Garden Beds and Planters for Soil
- Measure inside planter dimensions: Always measure the interior soil-contact walls. A bed constructed from 2-inch lumber will have internal dimensions 3 to 4 inches smaller than outer framing.
- Measure true soil depth: Leave 1 to 2 inches of freeboard below the top rim of your planter so soil and water do not overflow during heavy rain.
- For round planter barrels: Measure inside diameter across the top, divide by 2 for the radius, and calculate: 3.14 × Radius² × Depth in feet.
- Account for soil compaction: Loose bagged potting mix and fresh bulk compost contain tremendous air space. After initial watering, soil settles down by 10% to 15%.
- Layer deep beds with organic core ("Hugelkultur"): In beds deeper than 18 inches, fill the bottom 40% with logs, branches, and compostable yard waste to reduce soil cost while promoting fungal root health.
- Incorporate organic matter and soil amendments: Pure topsoil lacks porosity for container beds. For best vegetable yields, blend 50% screened topsoil, 30% aged organic compost (mushroom compost or well-rotted manure), and 20% coarse perlite or peat moss to provide aeration and nutrient storage.
- Layer deep metal beds with Hugelkultur: If your raised beds are 18 to 30 inches deep, filling the entire volume with premium bagged potting mix is unnecessarily expensive. Fill the lower 40% with rotting logs, tree limbs, dry leaves, and grass clippings. As the wood slowly breaks down over years, it acts as a sponge holding deep moisture and beneficial mycorrhizal fungi.
How Garden Soil is Calculated (Worked Example)
Consider filling two standard 8 ft long by 4 ft wide cedar raised garden beds at a 12-inch soil depth:
- 1. Single Bed Footprint: 8 ft × 4 ft = 32 sq ft.
- 2. Volume per Bed: 32 sq ft × (12 ÷ 12 ft) = 32.0 cubic feet.
- 3. Total for Two Beds: 32 × 2 = 64.0 cubic feet.
- 4. 12% Settling & Compaction Allowance: 64 × 1.12 = 71.68 cubic feet.
- 5. Converting to Cubic Yards: 71.68 ÷ 27 = 2.65 cubic yards.
- 6. Bags Needed (using 1.5 cu ft bags): 71.68 ÷ 1.5 = 47.78 -> 48 bags.
- 7. What to Buy: Buy 48 bags (1.5 cu ft size) OR order 3.0 bulk cubic yards of enriched garden blend soil (e.g. 50% topsoil, 30% compost, 20% peat/perlite) delivered to your driveway.
Popular Raised Bed Dimensions & Bag Soil Requirements
| Bed Dimensions (L × W × D) | Volume (Cu Ft) | Cubic Yards | 1.5 Cu Ft Bags (with Settling) |
|---|---|---|---|
| 4 ft × 4 ft × 6 in | 8.0 cu ft | 0.30 cu yd | 6 Bags |
| 4 ft × 4 ft × 12 in | 16.0 cu ft | 0.59 cu yd | 12 Bags |
| 8 ft × 4 ft × 10 in | 26.7 cu ft | 0.99 cu yd | 20 Bags |
| 8 ft × 4 ft × 12 in | 32.0 cu ft | 1.19 cu yd | 24 Bags |
| 10 ft × 3 ft × 18 in | 45.0 cu ft | 1.67 cu yd | 34 Bags |
Frequently Asked Questions About Soil Calculator
What is the best soil recipe for raised garden beds?
The premier all-around raised bed mix is "Mel's Mix" or a 3-way blend: 1/3 quality compost (cow manure, worm castings, leaf mold), 1/3 peat moss or coconut coir (for moisture retention), and 1/3 coarse vermiculite or perlite (for aeration and root expansion).
Why should I never fill a raised bed with standard yard dirt?
Native ground soil is heavy and contains clay and silt particles that compact into dense, airless mud inside container walls. Raised beds require high-porosity potting blends to allow rapid root development and drainage.
How much does a cubic yard of topsoil weigh?
A cubic yard of typical topsoil weighs approximately 2,000 to 2,200 pounds (about 1 ton) when moderately moist. When completely waterlogged after rain, a yard can weigh up to 2,700 pounds.
How do I calculate soil for a round barrel or planter pot?
Measure the diameter in feet across the circular rim, divide by 2 to find the radius, and multiply: 3.14159 × Radius × Radius × Depth (in feet). For example, a 2 ft diameter barrel that is 1.5 ft deep holds 3.14 × 1 × 1 × 1.5 = 4.7 cubic feet of soil.
How much does soil settle after the first watering?
Freshly bagged or bulk tilled soil fluffs up with air pockets during shoveling. After the first 2 or 3 thorough soakings, it will settle down by 10% to 15%. Always mound your beds 1 to 2 inches higher than the desired final level.
What is the difference between topsoil, garden soil, and potting mix?
Topsoil is native screened earth mined from agricultural land, heavy and mineral-rich. Garden soil is topsoil enriched with organic compost for in-ground planting. Potting mix contains zero native soil, consisting entirely of lightweight peat moss, composted bark, perlite, and vermiculite designed for drainage in container planters.