Crushed Stone Calculator
Works out crushed stone for a base, a drive or a drainage layer. Angular stone is the structural aggregate — it locks together under compaction, which is why it goes underneath things rather than on top.
Includes the waste allowance — this is the figure to order.
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The formula
volume = length × width × depth × (1 + waste) weight = volume × bulk density
The geometry is trivial; the bulk density is where the answer actually comes from. Crushed stone runs about 1600 kg per cubic metre loose, so a cubic metre weighs roughly 1.60 tonnes. Suppliers quote one or the other, which is why both are given.
What to watch out for
Depth depends entirely on what goes over it:
- Under a driveway: 100–150 mm, compacted in two layers rather than one.
- Under a patio or path: 75–100 mm.
- As a drainage layer: clean stone with no fines, usually 100 mm or more, and it must not be mixed with anything that will block the voids.
Stone with fines in it — MOT Type 1 and similar — compacts to a hard surface and sheds water. Clean, single-sized stone stays open and drains. They look similar in a photograph and do opposite jobs.
Frequently Asked Questions
How much crushed stone do I need?
Length × width × depth gives the volume; crushed stone runs about 1.6 tonnes per cubic metre. A 5 × 3 m area at 100 mm is 1.5 m³, around 2.6 tonnes with waste.
What is the difference between crushed stone and gravel?
Crushed stone is mechanically broken, so the pieces are angular and lock together under compaction. Gravel is naturally rounded by water and stays loose. Angular stone goes under things; rounded gravel goes on top.
How thick should a crushed stone base be?
100–150 mm under a driveway, 75–100 mm under a patio. Compact it in layers of no more than 75 mm — a single thick layer never compacts properly all the way down.