Formula
Volume is length times width times depth, with the depth in millimetres divided by 1000. Waste multiplies it by one plus the percentage.
Tonnes are cubic metres times the loose density in tonnes per cubic metre.
Bulk bags are the tonnes divided by the weight of one bag, rounded up.
Worked example
5 m by 4 m at 100 mm is 2.000 m³, and 2.200 m³ with 10% waste.
At 1.6 t/m³ that weighs 3.520 tonnes: 4.4 bulk bags, rounded up to 5 of 0.8 t.
Assumptions
Densities are loose, as delivered. Compacted sub-base weighs more per cubic metre once it is rolled.
Wet sand weighs more than dry sand. A supplier selling by the tonne will usually load to weight, not volume.
UK bags start at 800 kg and Australian bags at 1 tonne. Older UK catalogues list 850 kg bags.
Checked
Checked 11 November 2026. Wickes lists sharp sand and ballast jumbo bags at 800 kg, covering about 10.6 m² and 9.7 m² at 50 mm; those work back to about 1.5 and 1.65 t/m³. Bunnings Trade lists a 1 tonne bulk bag of brickies sand. The gravel and topsoil densities are the same assumptions as the Gravel and Topsoil pages.