Gravel Subbase Calculator
Calculate gravel volume, weight in short tons and metric tons, and haul cost — with compaction factor and multiple material types.
Gravel / Subbase
Granular fill, subbase, and crusher run calculations
Inputs
1.15–1.25 typical (loose volume ÷ compacted)
Delivered — ask supplier for current tonne price
Results
How to Use the Gravel Subbase Calculator
Enter the area length and width, the required compacted depth, and select the material type. The calculator applies a compaction factor to compute the loose volume needed to achieve the specified compacted depth, then converts to weight in short tons and metric tons. Add a unit cost for total material cost.
How It Calculates
Loose Volume = Compacted Volume × Compaction Factor
Weight (tons) = Loose Volume × Material Density (tons/cu yd)
Material densities (approximate): Crusher run 1.50, Granular A 1.45, Clear stone 1.35, Sand 1.40, Pit run 1.55 short tons per cu yd.
What to Know Before You Calculate
- Compacted depth is the target: The depth you enter should be the final compacted depth required by your design, not the initial loose-dumped depth.
- Compaction factor varies: Poorly graded materials compact more than well-graded. If your supplier provides a swell factor, use that — otherwise 1.25–1.30 is conservative.
- Lift thickness limits: Do not place more than 6–8 inches of loose material per compaction lift. Multiple lifts produce better compaction than one thick layer.
- Soil bearing under gravel: Subbase improves load distribution but does not fix soft or unstable subgrade. Assess the native soil before specifying subbase thickness.
Common Mistakes
- Ordering loose volume equal to compacted volume. Loose material compacts 20–30%. Order the loose volume (compacted volume × compaction factor) or you will run short.
- Not testing compaction. Specifying the right depth without verifying compaction allows soft spots under the slab that cause cracking.
- Mixing material types. Do not mix clear stone with crusher run unless designed for drainage. Mixed gradation changes bearing capacity.
- Leaving gaps at the perimeter. Subbase must extend to the full slab edge, including under any thickened-edge sections.
Frequently Asked Questions
How deep should gravel subbase be under a concrete slab?
Minimum compacted gravel depth under residential slabs is typically 4 inches (100 mm). In frost-prone areas or poor soil conditions, 6–12 inches or more may be required. Driveways and heavy-load areas often need 8–12 inches of compacted granular base.
What type of gravel is used under a concrete slab?
Crusher run (granular base) or Granular A is the most common subbase material for concrete slabs. Clear stone (washed) is used where drainage is critical. Avoid using topsoil or organic material as subbase — these compress and cause slab cracking.
How do I convert gravel cubic yards to tons?
Multiply cubic yards by the material density. Crusher run: ~1.5 tons/cu yd. Clear stone: ~1.35 tons/cu yd. Sand: ~1.4 tons/cu yd. Weights vary by moisture content and gradation. Get the supplier's certified unit weight for precision.
What is the compaction factor for gravel subbase?
Granular materials compact during placement. A typical compaction factor is 1.25–1.30 — meaning you need 25–30% more loose material to achieve the required compacted depth. This calculator applies the compaction factor to your loose volume calculation.
Related Calculators
- Concrete Slab Calculator
- Excavation Calculator
- Rigid Foam Insulation Calculator
- Vapour Barrier Calculator
Disclaimer: Material volumes and weights are estimates. Actual compaction factors and material densities vary by product, moisture content, and equipment. Verify subbase depth requirements with your geotechnical report or local building official.
Ready to build your estimate?
Open Full Estimator →