Free trap rock driveway calculator (tons)
Estimate tons of trap rock (dense crushed volcanic/igneous aggregate) for a driveway surface or base layer. Default densities (~100–120 lb/ft³) are planning only — quarries and moisture vary. For a hot-mix asphalt layer on top, use the asphalt calculator or driveway asphalt tool. Related: gravel / asphalt base calculator.
Notes
Trap rock is dense crushed volcanic or other igneous rock sold as driveway gravel, base stone, or a dressed surface. Angular faces lock under compaction better than many rounded river gravels — but density, size, and fines still depend on the quarry blend you actually buy.
Formula matches our base and asphalt tools: volume (ft³) × density ÷ 2000, then waste. A common residential planning thickness for a trap-rock surface or base lift is often in the 3–4 inch compacted range (more on soft soils or steep grades) — follow your contractor or engineer.
Confirm density and gradation with your quarry before ordering. Next: estimate asphalt tons on the main asphalt calculator, size a crushed-stone base with the asphalt base / gravel calculator, or read the trap rock driveway guide.
FAQ
How many tons of trap rock do I need for a driveway?
Multiply length × width × (thickness in inches ÷ 12) × density, then divide by 2,000. A 50 × 10 ft driveway 4 inches thick at 110 lb/ft³ needs about 9.17 tons, or 9.63 tons with 5% extra.
What density should I use for trap rock?
The calculator defaults to 110 lb/ft³ and offers planning values from 100 to 120 lb/ft³. Density, size and fines depend on the quarry blend and moisture, so confirm with your quarry.
How thick should a trap rock driveway be?
A common residential planning thickness for a trap rock surface or base lift is about 3 to 4 inches compacted, more on soft soils or steep grades. Follow your contractor or engineer.
What is trap rock?
Trap rock is dense crushed volcanic or other igneous rock sold as driveway gravel, base stone or a dressed surface. Its angular faces lock together under compaction better than many rounded river gravels.