Gravel & aggregate calculator

Aggregate is heavy and ordered by the tonne, so getting the amount wrong means either a half-covered area or a pile of spare stone blocking the drive. This calculator works out how much gravel, Type 1 or sand you need in tonnes, cubic metres and bulk bags. Here's how it's worked out.

How to work out how much aggregate you need

It's the area times the depth to get a volume, then the volume times the material's density to get a weight.

Tonnes = area × depth × density.

A 5m by 4m area (20 square metres) at 50mm deep is 1 cubic metre. As gravel weighs about 1.75 tonnes per cubic metre, that's roughly 1.75 tonnes. The calculator works the volume out from your sizes and applies the density for the material you pick.

What depth to use

The depth depends on the job.

• Decorative gravel: 40 to 50mm is enough to cover the ground well.
• Patio sub-base: around 100mm of compacted MOT Type 1.
• Driveway sub-base: 150mm or more, since it carries vehicles.

Converting cubic metres to tonnes

Each material has its own bulk density, so the same volume weighs a different amount depending on what it is. These are the rough figures the calculator uses.

These vary with grading and how wet the material is, so treat them as close estimates and check with your supplier for anything critical.

Bulk bags or loose by the tonne?

Bulk bags, sometimes called dumpy bags, hold around 0.8 tonnes each, though it varies. They suit smaller jobs and are easy to handle. For larger quantities, loose aggregate tipped and delivered by the tonne is usually cheaper per tonne. The calculator shows the bags so you can compare.

Order extra for compaction

A sub-base is laid loose and then compacted with a wacker plate or roller, which reduces its volume, so order about 10 to 15% more than the finished depth suggests. Loose decorative gravel that isn't compacted doesn't need that extra, so the straight calculation is fine there.

From materials to a priced job

Aggregate is one line on a groundwork job; the rest is labour, the finished surface and the machinery. Price the whole thing with how to price a job so you actually make a profit, drop the materials into a clean, itemised quote with the quote generator, and for a patio the paving calculator works out slabs, sub-base and bedding together.

This tool is for general estimating and gives approximate quantities. Densities and bag weights vary, so check with your supplier and your own measurements, and order a sensible amount over rather than exactly to the calculation.