How to calculate gravel and crushed rock for paths and driveways
When planning a driveway, pathway, or patio sub-base, quarry materials like crushed rock, roadbase, and drainage gravel are sold by weight in tonnes rather than volume. To calculate what you need, first calculate the cubic metres by multiplying length by width by compacted depth.
Density varies by stone type. Compacted crushed rock or roadbase typically weighs approximately 1.6 to 1.7 tonnes per cubic metre, whereas lighter volcanic scoria or drainage gravel may weigh 1.2 to 1.4 tonnes per cubic metre. Always check with your local landscape supply yard.
Compaction is the factor most people overlook. When you run a vibrating plate compactor over loose roadbase, the volume will reduce by 15% to 20% as smaller fines interlock with larger stones. Allow for this extra depth during your initial excavation.