How do I work out how much crushed stone I need?

Multiply the area (length times width) by the depth to get the volume, then multiply the volume by the material bulk density to get the mass. The calculator does this automatically and converts the result into tonnes, US tons, bags and a cost estimate.

How many tonnes of crushed stone are in a cubic metre?

It depends on the material. Crushed stone is roughly 1.6 tonnes per cubic metre, MOT Type 1 sub-base is about 2.1 tonnes, and slate chippings are nearer 1.3 tonnes. The tool uses the correct bulk density for the material you select, or your own custom figure.

What depth of aggregate should I lay?

For a decorative gravel surface 40 to 50 mm (about 2 inches) is typical. A driveway sub-base usually needs 100 to 150 mm of compacted MOT Type 1, plus a top layer. Always check the spec for your project — deeper layers need proportionally more material.

Why does the calculator add a waste allowance?

Loose aggregate compacts under traffic, some is lost to spillage and uneven ground absorbs a little extra. A 5 to 10 percent allowance means you order enough in one go rather than running short. You can set the percentage yourself.

Should I buy bags or bulk?

For small jobs bags are convenient, but per tonne they are far more expensive than a bulk bag (typically 850 kg to 1 tonne) or a loose load. The calculator shows both the bag count and the bulk tonnage so you can compare.

Is anything I enter uploaded or stored?

No. Every calculation runs entirely in your browser using JavaScript. No measurements, prices or results are ever sent to a server.

Crushed Stone Calculator

A crushed stone and aggregate calculator that turns three simple measurements — your area, the depth you want to fill and the material — into the exact tonnes (or US tons), the volume, the number of bags and an instant cost estimate. It is built for anyone ordering aggregate for a driveway, garden path, patio sub-base, French drain, shed base or border: landscapers sizing a delivery, DIYers comparing bagged versus bulk prices, and builders pricing up a sub-base before they call the quarry. Both metric and imperial units are supported, rectangular and circular areas are handled, and every step of the maths is shown so you can sanity-check the number before you part with money.

How it works

The calculator works in three stages. First it converts your measurements to a common base and computes the coverage area — length times width for a rectangle, or π × radius² for a circle. It multiplies that area by the depth (entered in cm or inches) to get a raw volume in cubic metres. Second, it applies your waste allowance so the order survives compaction and spillage, then multiplies the adjusted volume by the material’s bulk density to get the mass. That mass is reported as metric tonnes, US short tons, cubic yards and — if you give a bag size — a rounded-up bag count. Third, if you enter a price it multiplies the billable tonnage by your price per tonne, adds any flat delivery charge and shows an itemised total.

Each material carries a realistic loose bulk density: crushed stone around 1,600 kg/m³, MOT Type 1 sub-base around 2,100 kg/m³, ballast around 1,750 kg/m³ and slate chippings around 1,300 kg/m³. If your supplier quotes a different figure you can type a custom density and it overrides the preset.

Worked example

Say you are laying crushed stone over a 5 m by 4 m area to a depth of 5 cm. The area is 5 × 4 = 20 m². The raw volume is 20 × 0.05 = 1.0 m³. Add a 5 percent waste allowance and you need about 1.05 m³. At a bulk density of 1,600 kg/m³ that is 1.05 × 1600 = 1,680 kg, or 1.68 tonnes. At a price of £45 per tonne the material costs about 1.68 × 45 = £75.60, before any delivery charge. If your supplier only sells 25 kg bags, that is 1680 ÷ 25 ≈ 68 bags — which is exactly the moment most people switch to a bulk bag instead.

Reference: bulk densities and units

The mass of aggregate depends entirely on its bulk density — the mass of loose material per unit volume, before compaction. As a quick reference: crushed stone and washed gravel sit around 1.6 to 1.7 t/m³, sharp sand around 1.6 t/m³, MOT Type 1 sub-base around 2.0 to 2.1 t/m³, and lightweight slate chippings around 1.3 t/m³. One cubic metre equals about 1.308 cubic yards, and there are 27 cubic feet in a cubic yard. A metric tonne is 1,000 kg; a US short ton is about 907 kg, which is why the imperial tonnage reads slightly higher for the same load. These are loose figures — once compacted, a sub-base occupies noticeably less volume, which is another reason to keep a sensible waste allowance.

Everything here is an estimate to help you place an order with confidence. Always confirm the exact density and bulk-bag weight with your supplier, and round up rather than down so you are not held up mid-job by a short delivery.