Your Result Explained: Exact Takeoff Breakdown
A 15 ft × 20 ft rectangle covers exactly 300 square feet—a common footprint for a backyard vegetable garden plot, a new sod preparation bed, or a two-car patio sub-base. At a uniform 4-inch depth (0.3333 feet), a 300-square-foot area equals an exact geometric volume of 100.00 cubic feet. Divided by 27 cubic feet per cubic yard, you need 3.70 cubic yards (2.83 cubic meters) of material.
Using Screened Loam Topsoil (2,200 lbs/yd³ or 1.10 tons/yd³) as the baseline material, 3.70 cubic yards weighs 8,148 lbs, or 4.07 US short tons (typical moisture range: 3.70 to 4.44 tons). If you were to buy this same 100-cubic-foot volume in bags at a retail store, you would need 134 standard 0.75 cu ft topsoil bags, 100 bags at 1.0 cu ft, 50 mulch bags at 2.0 cu ft, or 200 stone/sand bags at 0.5 cu ft.
Ordering 3.70 cubic yards (usually rounded up to a 4-yard bulk order) of screened topsoil at $38/yd³ costs roughly $140.60 to $152.00 plus a single dump-truck delivery fee ($75–$100). Buying 134 retail 0.75 cu ft bags at $3.98 each would cost $533—making bulk delivery more than $300 cheaper.
Step-by-Step Math: 15 ft × 20 ft Area at 4" Depth
Converting a 15 ft by 20 ft (300 sq ft) rectangle at 4 inches deep into cubic feet, cubic yards, tons of topsoil, and retail bags.
- Surface Area: 20 ft × 15 ft = 300.00 sq ft (27.87 sq m).
- Depth in Feet: 4 inches ÷ 12 = 0.3333 ft (1/3 of a foot).
- Net Volume in Cubic Feet: 300 sq ft × (4 ÷ 12) = 100.00 cu ft.
- Volume in Cubic Yards: 100.00 cu ft ÷ 27 = 3.70 cubic yards (2.83 cu m).
- Weight as Screened Topsoil (2,200 lbs/yd³): 3.7037 yd³ × 2,200 = 8,148 lbs (4.07 US tons).
- Bag Counts for 100.00 cu ft: 134 bags (0.75 cu ft), 100 bags (1.0 cu ft), 50 bags (2.0 cu ft), or 200 bags (0.5 cu ft).
Bottom Line: A 15×20 area at 4 inches deep is 100 cubic feet or 3.70 cubic yards net (order 4.0 cubic yards to allow ~8% for settling).
How This Scenario Is Calculated
Multiplying 20 feet by 15 feet produces 300 square feet. Because 4 inches is exactly one-third of a foot (4 ÷ 12 = 1/3), multiplying 300 square feet by 1/3 foot yields a clean 100.00 cubic feet. Dividing 100 by 27 cubic feet per cubic yard gives 3.7037 cubic yards (rounded to 3.70 yd³).
Or, using the 324 shortcut formula: (300 sq ft × 4 in) ÷ 324 = 1,200 ÷ 324 = 3.70 cubic yards. Multiplying 3.7037 yd³ by 1.10 tons/yd³ for screened topsoil yields 4.07 US tons, while dividing 100 cu ft by 0.75 cu ft per bag rounds up to 134 bags.
Net Cubic Yards = [ Area (sq ft) × Depth (inches) ] ÷ 324 Cubic Yards = [ Length (ft) × Width (ft) × (Depth (in) ÷ 12) × (1 + Waste%) ] ÷ 27 Cubic Yards = [ π × (Diameter (ft) ÷ 2)² × (Depth (in) ÷ 12) ] ÷ 27 Project-Specific Tips & Common Mistakes
Order 4 Full Cubic Yards If Using Loose Soil or Gravel
Because 3.70 cubic yards is net geometric volume (0% waste), ordering an even 4.0 cubic yards gives you an automatic 8% buffer (8 extra cubic feet) to compensate for soil settling after watering or gravel compaction under a tamp.
Compare Material Weights for a 3.70-Yard (15×20×4") Project
While the volume of a 15×20×4" space is always 3.70 cubic yards, its weight changes dramatically by material: Hardwood Mulch = 1.11 tons (2,222 lbs); 50/50 Garden Blend = 2.96 tons (5,926 lbs); Screened Topsoil = 4.07 tons (8,148 lbs); #57 Gravel = 5.00 tons (10,000 lbs); and Ready-Mix Concrete = 7.41 tons (14,815 lbs).
Rototill the Bottom 2 Inches Into Existing Clay
When adding 4 inches of new screened topsoil over heavy native clay across a 15×20 area, spread the first 2 inches (1.85 cubic yards) and rototill it into the top 2 inches of native soil to create a transition zone before spreading the final 2 inches on top.
Mistake Ordering 3.0 yards instead of 4.0 yards to save on rounded buckets
Recommended Fix: Dropping from 3.70 yards down to 3.0 yards leaves you 19 cubic feet short—reducing your actual coverage depth across the 15×20 area from 4 inches down to just 3.2 inches.
Mistake Attempting to mix 3.70 cubic yards of concrete by hand for a 15×20 slab
Recommended Fix: At 4 inches thick, a 15×20 concrete slab (3.70 yd³) requires 167 bags of 80-lb concrete mix (13,360 lbs of dry mix). Always order a ready-mix concrete truck for any slab over 1.5 cubic yards.
Reference Coverage Table (Screened Loam Topsoil (Dry to Field Moist))
Compare how coverage changes across common depths for Screened Loam Topsoil (Dry to Field Moist) (default planning density 2200 lbs/yd³):
| Depth | 1 Cubic Yard Covers | 1 Ton Covers | Yards / 100 sq ft | Tons / 100 sq ft | Bags (0.75 ft³) / 100 sq ft |
|---|---|---|---|---|---|
| 1 in | 324 sq ft | 294.5 sq ft | 0.31 yd³ | 0.34 tons | 12 bags |
| 2 in | 162 sq ft | 147.3 sq ft | 0.62 yd³ | 0.68 tons | 23 bags |
| 3 in | 108 sq ft | 98.2 sq ft | 0.93 yd³ | 1.02 tons | 34 bags |
| 4 in Active | 81 sq ft | 73.6 sq ft | 1.23 yd³ | 1.35 tons | 45 bags |
| 6 in | 54 sq ft | 49.1 sq ft | 1.85 yd³ | 2.04 tons | 67 bags |
| 12 in | 27 sq ft | 24.5 sq ft | 3.7 yd³ | 4.07 tons | 134 bags |
Reference Source: USDA NRCS Soil Quality Indicators (Bulk Density) & University of Minnesota Extension.
Frequently Asked Questions
How many cubic yards is a 15×20 area at 2, 3, or 6 inches deep?
For a 15×20 area (300 sq ft) net: at 2 inches deep it is 50.00 cu ft (1.85 cubic yards); at 3 inches deep it is 75.00 cu ft (2.78 cubic yards); at 4 inches deep it is 100.00 cu ft (3.70 cubic yards); and at 6 inches deep it is 150.00 cu ft (5.56 cubic yards).
How many tons of gravel do I need for a 15×20 area at 4 inches deep?
At 3.70 net cubic yards, #57 crushed stone (1.35 tons/yd³) weighs 5.00 US tons (10,000 lbs), and dense-graded crusher run (1.40 tons/yd³) weighs 5.19 tons (10,370 lbs). If you add a 10% compaction allowance (4.07 cubic yards), order 5.5 to 5.7 tons of gravel.
How many 2 cu ft bags of mulch cover a 15×20 bed at 4 inches vs. 3 inches?
At 4 inches deep (100 cu ft), a 15×20 bed takes exactly 50 bags of 2.0 cu ft mulch. At the more common 3-inch mulch depth (75 cu ft), a 15×20 bed takes 38 bags of 2.0 cu ft mulch (2.78 cubic yards).
Will 3.70 cubic yards of topsoil fit in a single dump truck delivery?
Yes. A standard single-axle landscape dump truck holds 5 to 6 cubic yards of topsoil (or up to 6–7 tons), so 3.70 to 4.0 cubic yards arrives in a single drop.
How large of a tarp do I need on my driveway for a 4-cubic-yard soil dump?
A 4-cubic-yard conical pile of topsoil or gravel spreads out to roughly 8 to 9 feet wide by 10 to 12 feet long and 3.5 feet high when tipped from a dump bed. Lay down at least a 12 ft × 16 ft heavy-duty tarp.