Dirt Calculator
Estimate cubic yards, tonnage, and dump truckloads of fill dirt. Accounts for mechanical compaction, natural settlement allowances, foundation grading slopes, and soil swell.
Fill Dirt & Soil Calculator
Calculates compacted volume, settling allowance, weight tonnage & dump truck loads
Uncompacted fill shrinks 15%–20% once tamped or settled
Net excavation: 14.81 yd³ (400 ft³) + 2.22 yd³ compaction
How to Calculate Fill Dirt: Accounting for Soil Settlement
When excavated soil is dumped from a truck, it contains substantial entrained air voids. As rain falls and gravity acts over subsequent months—or when mechanical vibratory plates roll the surface—those voids collapse. If you order the exact geometric volume of an excavation hole, your finished grade will end up 2 to 4 inches sunken below grade.
Worked Contractor Example: Filling a 40' × 20' Lawn Depression at 6" Depth
Suppose a property owner is repairing an eroded backyard hollow measuring 40 feet long by 20 feet wide with an average fill depth of 6 inches:
- Calculate surface area: 40 ft × 20 ft = 800 sq ft
- Calculate net geometric void volume: (800 sq ft × 6 in) ÷ 324 = 14.81 cu yds
- Add 18% compaction and natural settlement allowance: 14.81 × 1.18 = 17.48 cu yds
- Convert cubic yards to scale weight (2,200 lb/yd³): 17.48 cu yds × 1.10 tons/yd = 19.23 Tons
- Truckload calculation: 17.48 cu yds ÷ 10 yds/truck = 2 Tandem dump truckloads
Fill Dirt vs. Topsoil: Soil Horizons and Structural Integrity
Soil science breaks the earth into vertical stratigraphic horizons. Confusing topsoil with fill dirt can cause severe structural property damage:
Excavated from 12+ inches beneath the surface. Consists strictly of broken mineral rock, clay, silt, and sand. Contains 0% organic decomposing matter. Because there is no organic material to rot and dissolve, it will not collapse into void pockets over decades. Required for backfilling building foundations, retaining walls, swimming pools, and under concrete slabs.
The biologically active top 2 to 8 inches of ground. Contains organic matter, humus, plant roots, and active microorganisms. If used as deep structural fill under driveways or foundations, the organic components will rot and decompose under moisture, shrinking by up to 40% and causing severe foundation subsidence, cracked footings, and collapsed slabs.
Foundation Grading: Calculating Yardage for IRC R401.3 Compliance
Water accumulating around residential foundation walls creates hydrostatic pressure, causing basement leaks, cracked concrete blocks, and foundation shifting. The International Residential Code (IRC) Section R401.3 governs site grading:
"The ground immediately adjacent to foundation walls shall be sloped away from the building at not less than one unit vertical in 20 units horizontal (5-percent slope) for a minimum distance of 10 feet measured perpendicular to the face of the wall."
Worked Math: Correcting Negative Grade Along a 50-Foot Foundation Wall
Suppose a homeowner has flat or negative slope along a 50-foot rear foundation wall and needs to build a 6-inch downward grade wedge extending 10 feet out:
Mechanical Compaction Lifts & Equipment Selection
Achieving 95% standard Proctor density requires matching equipment to soil plasticity and placing dirt in controlled vertical lifts:
High impact force (up to 3,500 lbs/blow) kneads cohesive clay particles together in narrow utility trenches and around foundation walls.
High-frequency vibration (5,000+ vpm) agitates granular soil particles, allowing them to interlock tightly in 4-to-6-inch lifts.
Provides minimal compaction depth (under 1.5 inches). Suitable solely for seating new grass sod onto topsoil; never use for deep fill.
Dirt Calculator FAQs
How do you calculate how many cubic yards of dirt are needed?
Measure the area in feet and depth in inches. Multiply length (ft) by width (ft) to calculate square feet, multiply by depth in inches, and divide by 324 to find base cubic yards: (Length ft × Width ft × Depth in) ÷ 324 = Cubic Yards. Always add a 15% to 20% compaction factor because loose excavated dirt naturally settles and compresses once watered and tamped into place.
What is the structural difference between fill dirt and topsoil?
Fill dirt is inorganic subsoil excavated from beneath the biological topsoil layer (the B-horizon). It contains virtually zero organic matter, seeds, or decomposing humus. Because organic matter decomposes and creates voids that cause structural sinking, fill dirt is strictly required for building foundations, backfilling retaining walls, swimming pool fills, and grading slopes. Topsoil contains 5% to 15% organic matter and is used solely for the upper 2 to 4 inches of lawn and garden root zones.
How much does a cubic yard of dirt weigh?
Typical dry, loose fill dirt weighs approximately 2,000 to 2,200 pounds (1.0 to 1.1 US tons) per cubic yard. When moisture-conditioned and compacted, density rises to 2,400 to 2,600 lbs/yd³ (1.2 to 1.3 tons). Heavy excavated clay saturated with rainwater can exceed 2,700 to 2,800 pounds (1.35 to 1.4 tons) per cubic yard.
How many cubic yards of dirt are in a dump truck?
A standard single-axle dump truck carries 5 to 7 cubic yards (6 to 8 tons). A commercial tandem-axle 10-wheeler carries 10 to 12 cubic yards (12 to 15 tons). A tri-axle dump truck carries 14 to 16 cubic yards (18 to 22 tons). Deliveries are limited primarily by Department of Transportation (DOT) gross vehicle weight restrictions.
What is the IRC building code requirement for foundation dirt grading slope?
Section R401.3 of the International Residential Code (IRC) mandates that the ground adjacent to foundation walls must fall a minimum of 6 inches within the first 10 feet (a 5% downward slope away from the structure). If property boundaries or physical obstructions prevent a 10-foot slope, swales or French drains must direct water away from the foundation.
Why must fill dirt be compacted in shallow lifts?
Civil engineering specifications require fill dirt to be placed in shallow lifts no deeper than 6 to 8 inches before running a mechanical plate compactor or jumping jack rammer. If you dump 18 to 24 inches of loose dirt at once and roll the surface, only the top 3 to 4 inches become densified, leaving uncompacted loose soil underneath that will settle irregularly over time.
What is the difference between screened fill and unscreened fill?
Unscreened fill dirt is loaded directly from excavation sites and contains large rocks, heavy clay clumps, and tree roots. Screened fill dirt is processed through a mechanical rotating trommel screen to remove debris and stones larger than 1/2 or 3/4 inch, making it dramatically easier to spread, rake, and compact evenly around pipes and foundations.
How do you convert bank yards to truck haul loads?
Virgin soil in the ground occupies Bank Cubic Yards (BCY). When excavated by an excavator, soil particles separate and expand with entrained air, creating a swell of 20% to 30%. To estimate the number of dump trucks required to haul away an excavation hole, multiply the bank volume by 1.25 to obtain Loose Cubic Yards (LCY).
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