What counts as landscape rock?
Landscape rock is any loose stone used to cover the ground for looks and low upkeep: crushed granite, slate, marble chips, pebbles and lava rock. Unlike mulch it does not break down, so one good layer can last for years.
Planning the rest of the job? Use the River rock calculator and the Pea gravel calculator too.
How deep should it be?
What types of landscape rock are there?
Crushed granite
Angular pieces lock together and stay put.
Best for paths
Slate chippings
Flat, blue grey and modern. Lighter than most stone.
Best for contemporary beds
Marble chips
Bright white. Can raise soil pH over time.
Best away from acid loving plants
Lava rock
Very light and porous. Fewer tonnes cover the same area.
Best for roof terraces and planters
How does the calculation work?
Tonnes = area (m²) × depth (m) × density (t/m³)
A border 8 m by 1.5 m at 7.5 cm: 12 × 0.075 = 0.9 m³. In slate at 1.4 t/m³ that is about 1.26 tonnes.
Rock types weigh very different amounts. A cubic metre of lava rock weighs about half as much as the same volume of granite, so pick the right type before you order by the tonne.