How it is calculated
Area times layer depth gives the volume; an allowance is added because loose material settles when it is compacted and some is lost on delivery. Weight is the volume times the bulk density. Densities of dry, loose material are from Engineering ToolBox: sand 1,555 kg/m³, gravel 1,680, sand with gravel 1,730, loose dirt 1,250. If your supplier quotes a figure, choose “Supplier’s density”.
Volume = L × W × h × (1 + allowance)Weight, t = volume × bulk density ÷ 1000Bags = weight ÷ bag weight, rounded upExample
An area of 5 × 4 m at 15 cm deep is 3 m³. With a 10% compaction allowance you need 3.3 m³ of sand, about 5.1 t or 206 bags of 25 kg. Gravel for the same area: about 5.5 t.
Tips from practice
- Sand and gravel are sold by the cubic metre or by the tonne — ask which the price is for.
- Lay a sub-base in layers of 10–15 cm and compact each one.
- Wet sand weighs about a fifth more than dry sand.
Questions and answers
How much does a cubic metre of sand weigh?
Dry, loose sand weighs about 1.55 t per m³; damp sand about 1.9 t.
How much does a cubic metre of gravel weigh?
Usually 1.4–1.7 t depending on the grade; the calculator assumes 1.68 t/m³ for dry gravel.
How much should I allow for compaction?
For a sand or gravel sub-base, typically 10–20%.
Found a mistake in a formula? Write to [email protected]