Free Topsoil Quantity calculator with clear step-by-step results.
Bed volume is length by width by depth, multiplied by the number of beds, with a settlement allowance because loose-delivered topsoil consolidates by 10-20% once watered and walked on. Mass is derived from bulk density since suppliers often sell by the tonne rather than by volume.
Volume to order
m3 = length x width x depth x beds x (1 + settlement allowance)
Mass
Tonnes = volume m3 x bulk density t/m3
At least 150 mm for lawn, 200-300 mm for vegetable beds and 400 mm or more for deep-rooted shrubs. Raised beds over hard standing need the full rooting depth.
Moisture and organic content. A wet mineral topsoil can exceed 1.6 t/m3 while a dry, peat-rich blend may be under 1.0, so ordering by tonne without knowing the density is risky.