How this instrument works
Road base, also called base course, is the layer of compacted aggregate spread beneath a driveway, path, or pavement surface — it distributes vehicle and foot-traffic loads across a wider area and improves drainage under whatever finished surface sits on top of it. Because it's compacted heavily during installation (commonly to at least 95% relative compaction), it packs noticeably denser than loose, uncompacted aggregate of the same material.
This instrument converts an area and depth into a weight the same way as this site's other bulk-material calculators: volume in cubic feet, converted to cubic yards, multiplied by density to get tons. The built-in density default of 115 lb/ft³ is typical for compacted crusher-run road base, but the real figure commonly ranges from about 100 to 150 lb/ft³ depending on gradation and how thoroughly it's compacted — confirm with your supplier if precision matters for a large order, and adjust the Material density field accordingly.
Because compaction changes volume, the depth entered here should be the FINISHED, compacted depth the base layer is specified to reach — not the looser depth of material as it's initially dumped and spread, which settles down noticeably once a compactor or roller passes over it. Ordering slightly more than the exact calculated tonnage is common practice to cover minor sub-grade irregularities and spillage during placement.
- Enter Area to cover (sq ft) — the footprint the base layer needs to cover.
- Enter Base depth (in) — the finished, COMPACTED depth specified for the base layer, not the looser as-spread depth.
- Adjust Material density (lb/ft³) if your supplier specifies a figure other than the 115 default.
- Read Volume (cu yd) and Weight (US tons) beneath the inputs.
Worked example — a 500 sq ft driveway base, 4 in deep
Enter 500 into Area to cover (sq ft), 4 into Base depth (in), and leave Material density (lb/ft³) at its 115 default — a typical compacted crusher-run figure. Volume works out to 500 × (4 ÷ 12) = 166.6667 ft³, which is 6.1728 cubic yards after dividing by 27.
Weight (US tons) reads 9.5833 — that's 166.6667 cubic feet at 115 lb/ft³, giving 19,166.67 lb, divided by 2,000 to convert to US tons. This is the tonnage to order for a 4 inch compacted base under a 500 sq ft driveway.
Questions
What density should I use for road base?
115 lb/ft³ is a typical figure for compacted crusher-run road base, but the real number varies roughly from 100 to 150 lb/ft³ depending on the specific material's gradation (the mix of particle sizes present) and how thoroughly it's compacted during installation. For a large order where precision matters, ask your aggregate supplier for their specific product's density rather than relying on the default.
Should I use the compacted or loose depth for this calculation?
Use the finished, COMPACTED depth — the thickness the base layer is specified to reach after a compactor or roller has passed over it. Loose, freshly spread material sits noticeably higher and less dense than its final settled state, so using an as-spread depth instead would understate the actual weight of material needed to reach the specified finished thickness.
How is road base different from the site's general gravel calculator?
Road base specifically refers to compacted crusher-run material engineered as a sub-base layer beneath pavement or a driveway surface, typically denser than general bank-run gravel used for other purposes like drainage or fill. This instrument's default density (115 lb/ft³) reflects that denser road-base figure, while the general gravel calculator's default reflects looser bank-run gravel instead.
How thick should a road base layer be for a driveway?
It depends on the traffic the driveway needs to support and the underlying soil — a light-duty residential driveway commonly uses a base in the range of 4 to 6 inches compacted, while a driveway expecting heavier vehicles or built over softer soil may call for more. Check local practice or a paving contractor's recommendation for your specific soil and traffic conditions rather than assuming one thickness fits every driveway.
Do I need a separate top layer above the base course?
Often, yes — road base is typically a sub-surface structural layer, with a separate finished top layer (asphalt, a thinner decorative gravel, pavers, or a concrete slab) placed over it to create the actual walking or driving surface. This calculator handles only the base layer's own quantity; a top layer needs its own separate calculation.