Calculation Results
Required estimates based on your parameters:
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A fill dirt calculator sizes the total volume, weight, and retail bags of subsoil needed to raise grade levels, fill garden beds, or level backyard cavities. Incorporating compaction settling variables, it prevents material shortfalls during transport and installation.
Formula:
Volume (cu yds) = [Length (ft) × Width (ft) × Depth (in) ÷ 12] ÷ 27 × (1 + Compaction Factor)
Worked Example: Filling a 20 ft × 10 ft lawn cavity to a depth of 4 inches with standard soil (15% compaction) requires 2.84 cubic yards (approx 3.12 tons or 153 bags of 40 lbs).
How to Calculate Fill Dirt Sizing & Weights
Estimating dirt projects requires geometric cavity formulas and physical density factors. Undisturbed soils pack tightly; loose subsoil delivered by dump trucks contains air gaps which collapse upon compaction. Compaction, swell, and structural weight equations align with the Caterpillar Performance Handbook standards [1], US Bureau of Reclamation sitework manuals [2], and ASTM D698 laboratory dry compaction limits [3]. Correct volume planning prevents highway haulage violations and material shortfalls.
Fill Dirt Math & Sizing Equations
- Rectangular Volume (cu yd): Volume = (Length (ft) × Width (ft) × [Depth (in) ÷ 12]) ÷ 27
- Circular Volume (cu yd): Volume = (π × Radius² (ft) × [Depth (in) ÷ 12]) ÷ 27
- Compacted Volume Adjuster: Adjusted Volume = Volume × (1 + Compaction % ÷ 100)
- Dirt Weight Sizing (US Tons): Weight = Adjusted Volume × (Material Density ÷ 2000)
- Retail Bag Count: Bags = Weight ÷ Retail Bag Weight (lbs)
Step-by-Step Worked Sizing Example
A residential yard grading cavity measures 24 feet long by 15 feet wide and needs 3 inches of topsoil. We use a 15% compaction settling buffer, and select 40-pound retail bags.
1. Calculate flat area: 24 ft × 15 ft = 360 sq ft
2. Convert depth to feet: 3 inches ÷ 12 = 0.25 ft
3. Calculate raw cubic volume: 360 sq ft × 0.25 ft = 90 cubic feet
4. Convert to cubic yards: 90 ÷ 27 = 3.33 cubic yards (raw)
5. Apply 15% compaction adjustment: 3.33 × 1.15 = 3.83 cubic yards (needed)
6. Calculate weight: 3.83 yd³ × (2,200 lbs/yd³ density for dry loam) = 8,426 lbs (approx 4.21 US tons)
7. Calculate 40 lb bags count: 8,426 lbs ÷ 40 lbs = 211 retail bags
Soil Density & Compaction Factors Table
| Soil Material Class | Bulk Density (lbs/yd³) | Compaction/Settling | Common Use Case |
|---|---|---|---|
| Topsoil / Loam | 2,200 lbs/yd³ (1,305 kg/m³) | 10% - 15% | Lawns, gardens, sod bedding |
| Clay Soil | 2,700 lbs/yd³ (1,600 kg/m³) | 15% - 20% | Structural fill, pond lining |
| Sand & Clean Gravel | 2,900 lbs/yd³ (1,720 kg/m³) | 8% - 12% | Drainage courses, sub-bases |
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