How to Calculate Select Fill Dirt
Calculate cubic yards, tons, and costs for select fill dirt projects. Includes compaction factors and engineering specifications for accurate estimates.
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The Formula
Multiply length, width, and depth in feet to get cubic feet. Divide by 27 for cubic yards. Always add 10-20% for compaction based on project type.
Measure Accurately
Measure in feet. For depth, measure in inches and our tool handles the conversion (divide by 12).
Check Your Shape
Most how to-calculate-select-fill-dirt projects are rectangles. If irregular, break it into smaller shapes.
Add Compaction
Select fill is engineered soil for structural applications. Getting calculations right prevents costly project delays and ensures stable foundations that meet building codes.
Planning a construction or landscaping project that requires select fill dirt? Getting your calculations right from the start can save you thousands of dollars and prevent frustrating delays. Whether you're preparing a foundation, building a driveway, or grading your property, knowing exactly how much select fill dirt you need is crucial for project success.
In this comprehensive guide, you'll learn everything about calculating select fill dirt accurately. We'll walk you through the exact formulas, show you how to account for compaction, explain the engineering specifications that matter, and help you avoid the costly mistakes that catch most DIYers and contractors off guard.
Let's dive into the world of select fill dirt calculations and ensure your project starts on solid ground with how to calculate select fill dirt the right way.
What is Select Fill Dirt and Why Accurate Calculation Matters
Select fill dirt isn't just any dirt you dig from your backyard. It's an engineered soil material specifically chosen and processed to meet strict quality standards for construction and landscaping projects.
Understanding Select Fill Dirt Composition
Select fill dirt consists of a carefully controlled blend of soil particles, typically including sand (50-70%), silt (20-30%), and clay (10-20%). Unlike regular fill dirt that can vary wildly, select fill is screened to remove rocks, debris, and organic matter. This balanced mixture compacts well, drains adequately, and provides stable support for structures.
Select Fill vs. Regular Fill Dirt
Select Fill
- • Screened and tested
- • Plasticity Index 4-10
- • ~1.21 tons/cubic yard
- • $15-40 per cubic yard
- • For foundations & structures
Regular Fill
- • Minimal processing
- • Variable composition
- • Inconsistent density
- • $8-20 per cubic yard
- • For general grading
Why Proper Calculation Saves Money
Calculating your select fill dirt needs accurately impacts your project in three critical ways: cost control, timeline management, and structural integrity. Ordering too little means expensive rush deliveries and project delays. Ordering too much means wasted money and disposal costs.
Professional contractors know that calculation errors compound quickly. A foundation project that settles due to insufficient material might require tens of thousands of dollars in remediation. Getting your calculations right the first time ensures your project performs correctly for decades.
How to Calculate Select Fill Dirt in 5 Simple Steps
Calculating select fill dirt becomes straightforward when you follow a systematic process. These five steps take you from raw measurements to an accurate order quantity.
The Complete Formula
All measurements in feet. Divide by 27 to convert cubic feet to cubic yards. Add compaction factor based on project type.
Step 1: Measure Your Project Area
- Rectangular: Length × Width × Depth (all in feet)
- Circular: π × Radius² × Depth (radius in feet)
- Triangular: 0.5 × Base × Height × Depth
Step 2: Calculate Volume in Cubic Feet
Example: 30ft × 20ft × 1.5ft = 900 cubic feet
Convert depth from inches to feet by dividing by 12 (6 inches = 0.5 feet).
Step 3: Convert to Cubic Yards
Divide cubic feet by 27: 900 ÷ 27 = 33.33 cubic yards
One cubic yard = 3ft × 3ft × 3ft = 27 cubic feet
Step 4: Add Compaction Factor (Critical!)
- Foundation Work: Add 15-20% (multiply by 1.15-1.20)
- Driveway Base: Add 12-15% (multiply by 1.12-1.15)
- Land Grading: Add 10-12% (multiply by 1.10-1.12)
Example: 33.33 yards × 1.15 = 38.33 cubic yards (round to 39)
Step 5: Convert to Tons (If Needed)
Multiply cubic yards by 1.21 to get tons
Select fill density: ~2,410 lbs/yd³ or 1.21 tons/yd³. Useful for delivery planning and weight calculations.
Understanding Compaction Rates for Select Fill Dirt
Compaction is where theory meets reality. When select fill arrives, it contains air pockets. As you compact the material, these air pockets collapse and soil particles reorganize into denser arrangement, reducing total volume by 10-20%. Learn more with our compaction calculator.
Foundation Work
Maximum compaction for structural loads. Requires 95-98% of maximum dry density.
Roads & Driveways
Substantial compaction for vehicle loads. Achieves 90-95% density.
Land Grading
Basic compaction for non-structural areas. Natural settlement acceptable.
Proper Compaction Method
- Place select fill in lifts no thicker than 6-8 inches (loose depth)
- Maintain moisture near optimum (8-12%) - material should form ball when squeezed but crumble when poked
- Use vibratory plate compactor for residential projects
- Make 3-6 passes over each lift, overlapping 6 inches
- Test compaction on critical projects (nuclear density gauge or sand cone test)
Select Fill Engineering Specifications
Plasticity Index (PI): 4-10
The Plasticity Index measures how soil behaves across moisture ranges. Quality select fill has PI between 4-10, meaning minimal volume change when wet or dry. This prevents heaving and cracking that high-PI materials cause.
Key Specifications
Particle Size
Screened to remove particles greater than 3 inches. Well-graded with range from coarse sand to fine silt for optimal compaction.
Moisture Content
Optimum: 8-12%. Too dry won't compact. Too wet creates muddy conditions and false density.
Density
~2,410 lbs/yd³ (1.21 tons/yd³) when properly compacted at optimum moisture.
Organic Content
Minimal to none. Organics decompose, causing settling and instability over time.
Common Calculation Mistakes to Avoid
❌ #1: Not Accounting for Compaction
The most costly mistake. Material volume reduces 10-20% during compaction. Always multiply by compaction factor before ordering.
❌ #2: Incorrect Unit Conversions
1 cubic yard = 27 cubic feet (not 9!). Converting 6 inches to 6 feet instead of 0.5 feet creates 12× error.
❌ #3: Ignoring Depth Variations
Sloped sites need depth measurements at multiple points. Using uniform depth on varied terrain dramatically underestimates needs.
❌ #4: Forgetting Existing Soil Conditions
Soft existing soil may compress under new fill weight. Poor soil might require excavation before filling, adding to total volume.
Select Fill for Different Project Types
Foundation & Building Pads
Most critical application. Requires:
- 18-24 inch minimum depth
- 95-98% compaction testing
- 15-20% compaction factor
- Building code compliance
Roads & Driveways
Requires stable base that resists rutting:
- 6-12 inch depth typical
- 12-15% compaction factor
- 6-8 inch lifts, thoroughly compacted
- Edge consideration for transitions
Utility Trenches
Confined space needs special attention:
- 15-18% compaction factor
- Protect utilities during compaction
- May use regular fill deep, select fill top
- Check utility owner specifications
Land Grading
Less critical if no structures:
- 10-12% compaction factor
- Consider future use
- Maintain drainage slopes
- Natural settlement acceptable
Estimating Select Fill Dirt Costs
Material Cost (2025)
- Select Fill (Screened) $15 - $40 / yd
- Regular Fill $8 - $20 / yd
- Structural/Engineered $25 - $45 / yd
Additional Costs
- Delivery (Local) $75 - $150
- Delivery (Regional) $150 - $300
- Compaction Testing $200 - $400 / test
Example: 30-Yard Foundation Project
- Material: 30 yards × $28/yd = $840
- Delivery: $125 (included for large order)
- Equipment Rental: $150 (plate compactor)
- Testing (if required): $400
- Total: $1,515
Installation Best Practices
Layering Technique: 6-8 Inch Lifts
Never place all material at once. Compaction equipment only densifies 6-8 inches deep. Always:
- Spread 6-8 inches loose depth
- Compact thoroughly (3-6 passes)
- Add next lift and repeat
- Thinner lifts (4-6 inches) near final grade
Moisture Management
Maintaining optimum moisture (8-12%) is critical:
- Squeeze test: Forms ball that crumbles when poked
- Add water with fine spray if too dry
- Spread thin or wait for drying if too wet
- Never compact saturated material
Equipment Selection
- Hand Tampers: Small areas under 50 sq ft
- Vibratory Plate Compactors: Most residential projects (recommended)
- Walk-Behind Rollers: Larger driveways, mid-size projects
- Ride-On Rollers: Commercial, roads, parking lots
When to Use Select Fill vs. Other Materials
Select Fill
Best For:
- ✓ Foundations
- ✓ Road/Driveway base
- ✓ Structural applications
- ✓ Utility trenches
Regular Fill
Best For:
- ✓ General grading
- ✓ Filling depressions
- ✓ Raising elevation
- ✓ Non-structural fills
Crushed Stone
Best For:
- ✓ Drainage systems
- ✓ French drains
- ✓ Behind retaining walls
- ✓ High water table areas
Frequently Asked Questions
How much select fill dirt do I need for a 20×30 area?
For a 20×30 foot area at 6 inches (0.5 ft) depth: 20 × 30 × 0.5 = 300 cubic feet ÷ 27 = 11.1 cubic yards. Add 15% compaction: 11.1 × 1.15 = 12.8 cubic yards. Order 13 cubic yards.
What's the difference between select fill and structural fill?
Select fill and structural fill often refer to the same engineered material. Both are screened, tested soil suitable for load-bearing applications. Always verify your supplier's product meets engineering specifications regardless of terminology.
How many tons are in a cubic yard of select fill dirt?
One cubic yard of properly compacted select fill weighs approximately 1.21 tons or 2,410 pounds at optimum moisture content. Multiply cubic yards by 1.21 to convert to tons.
Can I use select fill dirt for gardening or planting?
No. Select fill lacks organic matter and nutrients plants need. It's designed for structural stability, not plant growth. Use topsoil or compost-amended soil for gardens and planting areas.
How deep should select fill be for a concrete slab foundation?
Typical residential concrete slabs require 12-24 inches of select fill. Garage slabs: 12-18 inches. House slabs: 18-24 inches. Always follow engineering specifications for your specific project and soil conditions.
What is the best compaction method for select fill dirt?
Vibratory plate compactors work best for most residential projects. They compact 6-8 inch lifts effectively. Larger commercial projects use walk-behind or ride-on rollers. Always compact in lifts with 3-6 passes per layer.
Do I need to compact select fill in layers?
Yes. Compaction equipment only densifies 6-8 inches deep. Always place select fill in lifts (layers) no thicker than 8 inches, compact thoroughly, then add the next lift. This ensures uniform density throughout.
How long does it take for select fill dirt to settle?
Properly compacted select fill (95%+ maximum density) settles minimally, with 1-2% settlement in the first 6-12 months. Poorly compacted fill can settle 10-15% over years, causing structural problems.
Can I install select fill in the rain?
No. Rain increases moisture beyond optimum, preventing proper compaction. Wet select fill becomes muddy and won't compact correctly. Plan installation during dry weather and cover prepared areas if rain threatens.
What happens if I don't order enough select fill dirt?
Insufficient material causes project delays, rush delivery fees (50-100% premium), extended equipment rental costs, and potential quality issues from multiple batches. Building compaction factors into initial calculations prevents this.
Is select fill dirt the same as clean fill?
Not exactly. Clean fill is any contamination-free fill material. Select fill is a specific type of clean fill that's screened, tested to engineering standards, and has controlled particle distribution. All select fill is clean fill, but not all clean fill meets select fill specs.
How do I know if my select fill is good quality?
Quality select fill should be: uniform in color/texture, free from rocks >3 inches, screened to remove debris, damp but not soaked, and form a ball when squeezed that crumbles easily. Ask suppliers for test documentation showing Plasticity Index 4-10.
What equipment do I need to spread and compact select fill?
For residential projects: wheelb arrow or skid steer for moving, rake/shovel for spreading, vibratory plate compactor rental ($100-200/weekend), and garden hose for moisture management. Larger projects need bulldozers and rollers.
Can select fill be used for drainage applications?
Yes. Select fill's controlled gradation allows water percolation while providing structural support. It works well for utility trenches, French drains (with perforated pipe and gravel), land grading, and subsurface drainage systems.
How much does select fill dirt cost compared to regular fill?
Select fill costs $15-40/cubic yard depending on region, while regular fill runs $8-20/cubic yard. For a 30-yard project, select fill might cost $800-1,200 vs regular fill's $450-600. The premium ensures reliable structural performance.
