How Much Gravel Do I Need?
Gravel and decorative stone are sold either in bulk by the tonne or in pre-packed bags (typically 20kg or 25kg). Calculating the right amount before you order saves money and avoids multiple trips to the garden centre.
The calculation is: Volume (m³) = Length × Width × Depth. To convert to weight, multiply by the density of the material. Pea gravel, for example, has a density of around 1,600 kg/m³, so 1 m³ weighs approximately 1.6 tonnes. Crushed stone (MOT Type 1) is denser at around 1,900 kg/m³.
Bulk vs Bags
For areas larger than about 10 m², ordering bulk gravel by the tonne from a local builders' merchant or landscape supplier is almost always more cost-effective than buying bags. Most suppliers deliver in 0.5 or 1 tonne increments using a tipper lorry or bulk bag (also called a jumbo bag or tonne bag). For smaller areas or decorative projects, pre-packed bags from a garden centre are more convenient.
Weed Control
Before laying gravel, it is strongly recommended to lay a weed-suppressing membrane. This prevents weeds from growing through the gravel and significantly reduces long-term maintenance. The membrane does not affect the depth calculation — simply lay it first, then pour the gravel on top.