Landscaping
Gravel Calculator
Convert area and depth into cubic metres and tonnes for any gravel type.
How this calculator works
Enter the area to cover and your depth, and the calculator gives cubic metres with 10 percent added for settling and compaction. Gravel is sold by volume and delivered by weight, so it converts to tonnes using a density for your material.
Densities differ a lot: road base compacts to about 1.7 tonnes per cubic metre, decorative pebbles sit near 1.5, while lightweight scoria is only about 0.85.
Depth depends on the job. Decorative top layers need 40mm to 50mm, paths 75mm, and driveways or base layers 100mm or more, compacted in layers.
| Material | Density | 1m³ weighs |
|---|---|---|
| Road base | 1.7 t/m³ | about 1,700kg |
| Crushed rock 20mm | 1.6 t/m³ | about 1,600kg |
| Decorative pebbles | 1.5 t/m³ | about 1,500kg |
| Scoria | 0.85 t/m³ | about 850kg |
Suppliers may quote per tonne or per cubic metre. Use these densities to convert between the two.
| Use | Depth |
|---|---|
| Decorative ground cover | 40mm to 50mm |
| Garden paths | 50mm to 75mm |
| Driveway top course | 75mm to 100mm |
| Road base under paving | 100mm compacted |
| Driveway base course | 100mm to 150mm compacted |
Frequently asked questions
How many tonnes is a cubic metre of gravel?
Most crushed rock and gravel weighs 1.5 to 1.7 tonnes per cubic metre. Scoria is the light exception at about 0.85 tonnes per cubic metre.
What depth of gravel do I need?
For a decorative layer over weed matting, 40mm to 50mm. Paths want 50mm to 75mm. Driveways need a compacted base of 100mm to 150mm plus a 75mm to 100mm top course.
How much does gravel cost in Australia?
Bulk gravel typically runs $60 to $110 per cubic metre delivered as at July 2026. Plain road base sits at the cheap end, decorative pebbles at the expensive end and premium stones can exceed it.
Should I compact gravel?
Structural layers like road base must be compacted with a plate compactor in 50mm to 75mm lifts. Decorative top layers are just raked level. The 10 percent allowance in this calculator covers compaction loss.
What is the difference between road base and crushed rock?
Road base contains fines that bind when compacted, making a firm structural layer. Clean crushed rock has the fines screened out, drains freely and stays loose, better as a top layer or for drainage.
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