Gravel calculator
Two inches of gravel is a decorative dressing that shows the membrane through it within a season. Four inches is a path that stays put. A drive that carries a car wants six inches over a compacted sub-base, laid in two layers rather than one, because gravel dumped deep never consolidates properly in the middle.
Gravel is sold by weight but used by volume. One tonne of loose gravel is about 0.6 cubic metres and covers roughly 12 square metres at 50 mm deep. Multiply area by depth for volume, then multiply by a bulk density near 1.68 tonnes per cubic metre.
How to work out gravel
The number that surprises people is bulk density. Gravel is not solid rock; a loose heap is roughly 40% air, so a tonne occupies far more space than the same weight of stone would. Suppliers quote tonnes because that is what the lorry weighs, and garden centres quote litres because that is what the bag holds, which means the same job can be priced two incompatible ways. Converting between them is the whole point of this page. Bulk bags nominally hold 850 kg but arrive anywhere between 700 and 900 depending on how wet the stone was when it was filled.
Questions
About 12 square metres at 50 mm deep, or 130 square feet at 2 inches. Halve the coverage if you double the depth.