Free Gravel & Aggregate Calculator — Order in Tonnes

Work out how many tonnes of gravel, road base, crushed rock or sand to order. Enter your area and depth, and the calculator applies a compaction factor and material density to convert your measurements into an order in tonnes — the way quarries and landscape suppliers actually sell it.

How to use this calculator

Enter the length, width and depth of the area you're filling.
Check the compaction factor — compacted materials like road base need more loose material to reach your finished depth.
Check the density for your material — different aggregates weigh different amounts per cubic metre.
Read off your order in tonnes, rounded up to the next 0.5 t.

What this calculator assumes

Volume is calculated as area × depth, then increased by the compaction factor to give the loose volume you need delivered.
The density setting converts loose volume to tonnes — typical Australian aggregates range from roughly 1.2 t/m³ (some sands and soils) to 1.6+ t/m³ (road base and crushed rock). Confirm with your supplier.
Orders round up to 0.5 tonne increments, matching common supplier ordering.
Depth should be your finished, compacted depth — the calculator grosses it up for you.

Frequently Asked Questions (F&Q)

FAQ 1
Question: How many tonnes of gravel do I need?
Answer: Multiply area (m²) by depth (m) to get cubic metres, allow for compaction, then multiply by the material's density in tonnes per cubic metre. A 20 m² path at 100 mm deep in road base is around 3–3.5 t once compaction is included — this calculator does the conversion for you.

FAQ 2
Question: What is a compaction factor and why does it matter?
Answer: When you compact road base or crushed rock with a plate compactor, it loses volume — often 10–20%. If you order the exact finished volume, you'll come up short. The compaction factor grosses up your order so the compacted result hits your design depth.

FAQ 3
Question: How much does gravel weigh per cubic metre?
Answer: It varies by material and moisture: sands around 1.2–1.5 t/m³, road base and crushed rock commonly 1.5–1.6 t/m³ loose. Your supplier can give the exact figure for their product — enter it in the density field for a precise order.

FAQ 4
Question: What depth of road base do I need under a slab or paving?
Answer: Common domestic depths are 75–100 mm compacted under paths and paving, and 100 mm+ under driveways — but your plans, engineer or paving supplier's specification takes precedence. Enter the specified compacted depth and let the calculator gross it up.

FAQ 5
Question: Should I order in tonnes or cubic metres?
Answer: Most quarries and landscape yards price and load by the tonne, which is why this calculator outputs tonnes. If your supplier quotes in m³, the loose volume figure is shown too.