How to calculate gravel in tonnes
Tonnes = volume × density (t/m³)
Bulk bags = tonnes ÷ bag size
How deep should gravel be?
| Job | Typical depth |
|---|---|
| Decorative gravel border | 30 to 50 mm on membrane |
| Garden path | 40 to 50 mm on a compacted base |
| Gravel driveway top layer | 40 to 50 mm on 100 to 150 mm of compacted road base |
| Sub-base under a patio | 75 to 100 mm of compacted road base |
Worked example
A 6 m × 3 m driveway topped with 50 mm of gravel needs 0.9 m³, which is about 1.44 tonnes at 1.6 t/m³: 2 bulk bags of 1 tonne. A 150 mm road base layer under it is another 2.7 m³, about 5.7 tonnes. Landscape suppliers also sell by the tonne or cubic metre, delivered by truck.
Frequently asked questions
How much gravel do I need for a driveway?
For a 6 m by 3 m driveway with a 50 mm top layer, about 1.44 tonnes, or 2 bulk bags of 1 tonne.
How many tonnes is a cubic metre of gravel?
About 1.6 tonnes for most gravel and shingle, and around 2.1 tonnes for compacted road base.
How much does a bulk bag of gravel cover?
A 1 tonne bag of gravel covers about 12.5 m² at 50 mm deep, or about 20.8 m² at 30 mm.
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Last updated October 2026.