Gravel Calculator: Tonnes, Cubic Yards and Bulk Bags
Gravel is bought by weight or by bulk bag, but the calculation starts with volume: area × depth. Multiply that volume by the material's density to get tonnes, then work out how many bulk bags the delivery needs.
Density figures to use
- Loose gravel and pea shingle: about 1.4-1.6 tonnes per cubic metre.
- MOT Type 1 / crushed hardcore: about 1.9-2.1 tonnes per cubic metre when compacted.
- Sand: about 1.6 tonnes per cubic metre.
- A standard bulk bag holds roughly 0.5-0.6 m³, close to 850 kg for gravel.
How deep to lay it
- Decorative borders and beds: 40-50 mm.
- Footpaths: 50 mm over a compacted sub-base.
- Driveways: 50 mm of gravel over 100-150 mm of compacted MOT Type 1.
- Shallower than 40 mm and the substrate shows through; deeper than 75 mm and walking becomes difficult.
Compaction and edging
Sub-base material compacts by roughly 20-30% once rolled, so order the pre-compaction volume rather than the finished depth. Install edging before spreading, and lay a permeable geotextile membrane underneath to stop the stone migrating into the soil and to suppress weeds.
Key takeaways — Gravel Calculator
- Tonnes = area × depth × density; depth in metres, not millimetres.
- Order extra for compaction on sub-base layers.
- Use edging and a membrane to keep the finished surface stable.