How much gravel do I need?

Multiply the area to cover by the depth of gravel to get the volume in cubic metres, then multiply by the density to convert to tonnes, since gravel is usually sold by the cubic metre or tonne. A typical driveway gravel is around 1.5 tonnes per cubic metre.

What depth of gravel should I lay?

For a path, 50 to 75 millimetres is common; for a driveway, 100 to 150 millimetres over a compacted base. Deeper layers need more material, so getting the depth right matters as much as the area.

Is gravel sold by tonne or cubic metre?

Suppliers sell both, so it helps to know your need in each. This tool gives cubic metres and tonnes using the density you enter. Different aggregates have different densities, so check with your supplier for an exact figure.

Gravel and Aggregate Calculator

This calculator works out how much gravel or aggregate you need for a project in New Zealand, giving the answer in both cubic metres and tonnes so you can order whichever way your supplier sells it. Whether you are laying a gravel driveway, topping a path, building a base course under paving, or filling a drainage trench, getting the quantity right saves money and the hassle of either running short mid-job or paying to cart away a leftover pile. The maths is straightforward: the volume is the area you are covering times the depth of gravel, and because gravel is heavy, that volume is converted to tonnes using its density. You enter the length and width of the area, the depth in millimetres, and the density of the aggregate, and the calculator returns the volume in cubic metres and the weight in tonnes. As a guide, a path is usually fifty to seventy-five millimetres deep and a driveway one hundred to one hundred and fifty millimetres over a compacted base, while typical driveway gravel weighs around one and a half tonnes per cubic metre. Different aggregates vary in density, so confirm the figure with your supplier for an exact weight, and order a little extra for compaction and spreading. An estimate to plan your order.

Length (m)

Width (m)

Depth (mm)

Density (t/m³)

2.25 t

gravel needed by weight

Volume1.50 m³

Area15.0 m²

Densities vary by aggregate; confirm with your supplier. Order a little extra for compaction and spreading. An estimate for planning only.

How it works

The area is the length times the width. The volume is the area times the depth, with the depth converted from millimetres to metres by dividing by 1,000. The weight in tonnes is the volume times the density. Order a little more than calculated to allow for compaction.

Worked example

A 5 by 3 metre area is 15 square metres. At 100 millimetres deep that is 1.5 cubic metres, and at a density of 1.5 tonnes per cubic metre, about 2.25 tonnes of gravel.

Related calculators

Mulch and Bark: garden mulch.
Garden Bed Soil: soil volume.
Concrete Calculator: concrete volume.
Retaining Wall Blocks: wall blocks.

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