How to Calculate Soil for Your Project: Complete Guide
How to Calculate Cubic Yards of Soil
Calculating soil needs is essential for gardening, landscaping, and construction projects. Here's the step-by-step process:
- Measure your area - Determine length and width in feet
- Determine depth - How deep you need soil (convert inches to feet by dividing by 12)
- Calculate volume - Multiply length ร width ร depth to get cubic feet
- Convert to cubic yards - Divide cubic feet by 27
Formula:
Cubic Yards = (Length ร Width ร Depth) รท 27
Example: A 10ft ร 8ft garden bed with 6 inches (0.5 ft) depth needs: (10 ร 8 ร 0.5) รท 27 = 1.48 cubic yards
Raised Bed Soil Calculator Tips
Raised beds require more precise soil calculations because you're filling from the ground up:
- Standard depth: 12 inches - Suitable for most vegetables and herbs
- Deep beds: 18-24 inches - Best for root vegetables like carrots, parsnips, and potatoes
- Soil mix ratio: 60% topsoil, 30% compost, 10% potting mix or perlite for drainage
- Settlement allowance: Add 10% extra soil as beds settle over time
Common Raised Bed Sizes:
- 4' ร 4' ร 1' = 0.6 cubic yards (16 cu ft)
- 4' ร 8' ร 1' = 1.2 cubic yards (32 cu ft)
- 4' ร 8' ร 1.5' = 1.8 cubic yards (48 cu ft)
Topsoil vs Compost vs Garden Soil
Topsoil
Best for: Filling large areas, lawn top dressing, leveling yards
Density: 75 lbs/cu ft (heavier, mineral-rich)
Cost: $25-$40 per cubic yard
Note: May need amendments for growing vegetables
Compost
Best for: Soil amendment, enriching existing beds, mixing with topsoil
Density: 50 lbs/cu ft (lighter, organic matter)
Cost: $30-$55 per cubic yard
Note: Should be mixed with other soil (not used alone)
Garden Soil
Best for: Vegetable gardens, flower beds, in-ground planting
Density: 65 lbs/cu ft (balanced mix)
Cost: $35-$50 per cubic yard
Note: Pre-mixed blend of topsoil and compost
Potting Mix
Best for: Containers, raised beds, seed starting
Density: 40 lbs/cu ft (lightest, soilless mix)
Cost: $45-$75 per cubic yard (more expensive)
Note: Sterile, excellent drainage, contains peat/coco coir
Bulk Soil vs Bagged Soil: Cost Comparison
Should you buy soil in bags or order bulk delivery? Here's the breakdown:
Bulk Delivery
- โ More economical for projects over 1 cubic yard
- โ Less plastic waste - environmentally friendly
- โ Consistent quality - same batch throughout
- โ Time-saving - delivered to your driveway
- โ Delivery fee: $50-$150 depending on distance
- โ Minimum order: Usually 1-2 cubic yards
Cost: $25-$50 per cubic yard + delivery
Bagged Soil
- โ Convenient for small projects (under 1 cu yd)
- โ No delivery wait - immediate availability
- โ Easy storage - buy what you need
- โ Portable - transport in your car
- โ 2-3x more expensive per cubic yard
- โ Quality varies between brands/batches
Cost: $70-$150 per cubic yard (bagged equivalent)
Conversion Reference:
- 1 cubic yard = 27 cubic feet = 54 bags (0.5 cu ft each) = 13.5 bags (2 cu ft each)
- Cost comparison example: 1 cu yd bulk ($35) vs 14 bags of 2 cu ft ($5 each = $70)
How Much Does a Yard of Soil Weigh?
Soil weight varies significantly based on type, moisture content, and composition:
- Topsoil: 2,000-2,200 lbs per cubic yard (1-1.1 tons)
- Compost: 1,000-1,600 lbs per cubic yard (0.5-0.8 tons)
- Potting Mix: 800-1,200 lbs per cubic yard (0.4-0.6 tons)
- Garden Soil: 1,700-2,000 lbs per cubic yard (0.85-1 ton)
- Wet soil: Can be 25-40% heavier than dry soil
โ ๏ธ Important: A pickup truck bed typically holds 2-3 cubic yards maximum. For larger orders, consider delivery or multiple trips. A cubic yard of wet topsoil can weigh over a ton!
Soil Calculator for Different Shapes
Different garden shapes require different calculation formulas:
Rectangle/Square
Volume = Length ร Width ร Depth
Example: 10ft ร 6ft ร 0.5ft = 30 cu ft = 1.11 cu yd
Circle
Volume = ฯ ร Radiusยฒ ร Depth (ฯ โ 3.14159)
Example: Circle with 5ft radius and 0.5ft depth = 3.14 ร 25 ร 0.5 = 39.3 cu ft = 1.46 cu yd
Triangle
Volume = (Base ร Height รท 2) ร Depth
Example: Triangle with 8ft base, 6ft height, 0.5ft depth = (8 ร 6 รท 2) ร 0.5 = 12 cu ft = 0.44 cu yd
Irregular Shapes
For complex shapes, divide into simpler sections (rectangles, circles, triangles) and calculate each separately.
Tip: Add 10% extra for irregular areas to ensure adequate coverage
Common Soil Calculator Mistakes to Avoid
- โ Not converting inches to feet: Always divide inches by 12 before calculating. 6 inches = 0.5 feet, not 6 feet!
- โ Forgetting to account for settling: Soil compacts over time. Add 10-15% extra for raised beds and new garden areas.
- โ Using diameter instead of radius: For circles, remember radius = diameter รท 2. A 10ft diameter circle has a 5ft radius.
- โ Not accounting for existing soil: If you're amending existing soil rather than filling from zero, you need less material.
- โ Ordering exact amounts: Always round up. It's better to have a little extra than to run short mid-project.
- โ Mixing up cubic feet and square feet: Cubic feet is volume (3D), square feet is area (2D). You need depth for volume calculations.
When to Add Extra Soil
In these situations, order 10-25% more soil than your calculator results:
- Raised beds: +15% for settling over first season
- Clay soil areas: +20% for mixing and improving drainage
- Sloped terrain: +25% for uneven distribution
- Rocky existing soil: +15% to account for voids between rocks
- Large projects: +10% safety margin to avoid shortages
- Delivery minimum not met: Round up to supplier's minimum order
Soil Testing and Quality
Before ordering bulk soil, ask suppliers these critical questions:
- pH level: Most plants prefer 6.0-7.0 (slightly acidic to neutral)
- Organic matter content: 5-10% is ideal for gardens
- Screening: Is it screened? What size? (3/8" to 1/2" is standard)
- Source: Where does the topsoil come from? Avoid contaminated sites
- Weed seeds: Has it been composted hot enough to kill seeds? (131ยฐF+)
- Salt content: High salt can damage plants (important in coastal areas)
๐ก Pro Tip: Request a small sample before ordering bulk quantities. Test it with moisture (should crumble, not clump) and smell (should smell earthy, not sour or chemical).