The base math
Volume = length × width × depth. In Imperial cubic feet, divide by 27 for cubic yards. A 30 × 20 ft driveway at 4 inches deep:30 × 20 × (4/12) = 200 ft³ ÷ 27 ≈ 7.41 CY
Mass = volume × density. Density is product-specific (see table below). For 7.41 CY of crushed stone at 1.35 t/CY:7.41 × 1.35 ≈ 10.0 tons
Density reference
Loose density at moisture equilibrium. Compacted density runs 10-15% higher.
| Material | kg/m³ | lb/ft³ | tons/CY |
|---|---|---|---|
| Pea gravel | 1,680 | 105 | 1.42 |
| Crushed stone (3/4") | 1,600 | 100 | 1.35 |
| Sand | 1,520 | 95 | 1.28 |
| Recycled concrete | 1,600 | 100 | 1.35 |
| Road base / Class V | 1,920 | 120 | 1.62 |
These are typical values. Real density varies by moisture, particle size, and geology. Class V from one quarry will not match Class V from another. For mass-critical orders (drainage installs with weight limits, structural base courses), ask the supplier for their tested bulk density.
Picking depth
Driveways
- Residential, passenger vehicles: 4-6 inches of 3/4 inch crushed stone over compacted subgrade. Over clay subgrade in freeze-thaw climates, add a 4-inch base of larger stone underneath.
- Residential, light trucks (RVs, boats): 6-8 inches over compacted subgrade. Heavier base course (1.5-2 inch stone) at the bottom 3-4 inches.
- Commercial drives, regular truck traffic: 8-12 inches across multiple courses. Designed cross-section by a civil engineer for the expected loading.
French drains and drainage
Drainage applications use clean crushed stone (no fines that would clog the void space). Typical: 3-6 inches of 3/4 inch clean stone wrapped in geotextile fabric. Pipe bedding under sewers and water lines is usually 6 inches of clean stone above and below the pipe.
Road base course
Road base (Class V, Class 5, MnDOT 6 — designation varies by region) is a dense-graded aggregate compacted to 95-100% modified Proctor density. Typical road cross-sections call for 6-12 inches of base course; pavement designer specifies the layer thicknesses based on traffic loading and subgrade strength.
Compaction and waste
Loose gravel compacts under rolling. A loose cubic yard occupies roughly 0.85-0.90 cubic yards after compaction. Suppliers deliver in the loose state; the spec is usually for compacted thickness. Order enough loose volume to make the compacted thickness.
Practical: order 10-15% more than your bare geometric volume. That covers:
- Compaction loss (loose → compacted)
- Settling into a soft subgrade
- Spillage during placement
- Slight over-thickness at the placement plus margin
Cubic yards vs tons
Different suppliers price differently:
- Bulk quarry, large-volume: almost always priced by the short ton. They weigh trucks at the scale on the way out.
- Garden center, decorative stone: typically priced by the cubic yard. They scoop with a bucket loader and assume a standard bucket-to-CY conversion.
- Bagged retail: by the cubic foot or bag size. 0.5 CF bags are common; 27 bags make a cubic yard.
To compare quotes, convert everything to one unit. If supplier A quotes $25/CY and supplier B quotes $20/ton on the same crushed stone:
Supplier B equivalent = $20/ton × 1.35 t/CY = $27/CYSupplier A is cheaper at the same product. Always normalize.
Verifying delivery
On delivery, the truck driver will hand you a ticket with tons delivered, product, and date. Keep tickets with the bid file. Reconcile against your computed quantity:
- Computed tons match ticketed tons within 5-10% — normal.
- Computed tons under-shoot ticketed tons by 15%+ — driver over-loaded, or your math missed scope.
- Computed tons over-shoot ticketed tons — driver under-loaded, or subgrade compacted more than expected.
Over time these reconciliations calibrate your density assumptions for your specific suppliers and projects. That feedback loop is what separates a one-job estimator from a career estimator.