GardenCalcs.uk
Volume Calculator — Cubic Metres for Garden Projects
Work out volumes for any garden project in cubic metres or litres.
How We Calculate This
Rectangular: Volume = Length × Width × Depth. Cylindrical: Volume = π × Radius² × Depth.
Tapered: uses the prismoidal (pyramidal frustum) formula V = (Depth ÷ 3) × (A_top + A_base + √(A_top × A_base)) to account for sloping sides. The base is taken as 80% of both the top length and the top width.
An optional wastage allowance (default 0%) over-orders the headline volume to cover settling, compaction and spillage — add 10–15% for loose materials like topsoil or bark mulch.
Results are shown in cubic metres, litres (1 m³ = 1,000 L), and the approximate number of bulk bags assuming 0.7 m³ per bag.
Frequently Asked Questions
There are 1,000 litres in one cubic metre. So 0.5 m³ equals 500 litres.
A standard UK bulk bag (also called a tonne bag or dumpy bag) typically holds around 0.6–0.7 cubic metres of loose material, weighing roughly 850kg–1 tonne. This calculator assumes 0.7 m³ per bag. Sizes vary between suppliers — Rolawn standard bags are 0.5 m³ (500 L) and large bags 0.75 m³ (750 L) — so always confirm the bag volume before ordering.
It depends on the material. Topsoil weighs roughly 1.4 tonnes per m³, gravel about 1.8 tonnes per m³, and sand about 1.6 tonnes per m³.
Common depths: mulch 50-75mm, gravel paths 40-50mm, topsoil for lawns 150mm, raised beds 200-300mm.
1 cubic metre = 1,000 litres. So 0.5 m³ = 500 litres. This conversion is useful for ordering compost, soil, and gravel in practical quantities.
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Last updated: February 2026
All calculations are estimates based on standard gardening guidelines. Results may vary with soil conditions, climate, and plant varieties.