How Much Gravel Do I Need? Driveway, Path & Base Guide

Working out how much gravel you need is a two-step problem, and skipping the second step is the most common mistake. Step one is volume: the area you are covering multiplied by the depth of the layer. Step two is weight: that volume multiplied by the material's bulk density, because gravel, sand, and stone are almost always sold and delivered by the tonne, not by the cubic metre or yard. A pile that is the right volume but ordered by guesswork in weight can be a tonne short or a tonne over.

The gravel, sand and aggregate calculator does both steps: you enter the area and depth, choose the material, and it returns the volume in cubic metres and cubic yards and the weight in metric tonnes and US tons. This guide explains the depths to use for different jobs, why materials weigh such different amounts, and how to allow for compaction so your finished layer ends up at the depth you actually wanted.

Measure the area you are covering. For a rectangular driveway or path, that is simply length times width. For an irregular shape, break it into rectangles and triangles, work out each piece, and add them up; for a circular bed, multiply the radius by itself and by 3.14. Then choose a depth for the layer. Depth is where people most often under- or over-order, because the right depth depends entirely on what the gravel is for.

A decorative gravel mulch over landscape fabric is usually 40 to 50 millimetres (about 2 inches) — just enough to hide the fabric and suppress weeds. A gravel path is 50 to 100 millimetres. A patio or paving sub-base is around 100 millimetres of compacted granular material. A driveway sub-base that carries cars is 100 to 150 millimetres (4 to 6 inches) or more, often built in two layers of different stone sizes over a compacted formation. For anything structural, follow the pavement specification rather than a rule of thumb.

Multiplying area by depth gives you a volume, but the supplier's truck is loaded by weight. To convert, multiply the volume in cubic metres by the material's bulk density in tonnes per cubic metre. Loose dry gravel and crushed stone are roughly 1.5 to 1.7 tonnes per cubic metre, sand about 1.6, road base or ballast around 1.9 to 2.1, topsoil about 1.3, and bark mulch only about 0.4. So a cubic metre of road base weighs nearly five times as much as a cubic metre of mulch — which is why you cannot order 'a few tonnes' without knowing the material.

For example, a 10 by 3 metre driveway at 100 millimetres deep is 3 cubic metres. In gravel at 1.6 tonnes per cubic metre that is about 4.8 tonnes; in road base at 1.9 it is about 5.7 tonnes. The calculator lets you pick the material from a list of typical densities and shows the weight in both metric tonnes and US short tons, so you can order in whichever unit your quarry or landscape supplier uses. Bear in mind these are loose-dry figures — wet material is 10 to 25 percent heavier, so a rain-soaked delivery weighs more for the same volume.

Here is the step that catches people out. When you spread a granular sub-base and compact it with a roller or plate compactor, it settles — the finished compacted thickness is less than the loose thickness you tipped out. To end up with 100 millimetres of compacted sub-base, you need to order and spread noticeably more than 100 millimetres of loose material, commonly 20 to 30 percent more for granular sub-base. Enter that as the waste or compaction allowance in the calculator so the delivered weight reflects the loose volume, not the final compacted one.

Decorative gravel that is simply raked level and not compacted needs only a small allowance for spillage and for the gravel that works its way into the ground over time — 5 to 10 percent is plenty. The distinction matters: apply a compaction allowance to sub-base and road base, and a modest spillage allowance to loose decorative gravel. Getting this right is the difference between a driveway that finishes flush with its edging and one that sits low and needs a top-up load a week later.

Suppliers in the United States often quote gravel by the cubic yard, while UK, Australian, and Asian suppliers usually quote by the tonne. The calculator shows volume in both cubic metres and cubic yards and weight in both metric tonnes and US tons, so you can match whatever your supplier uses and avoid a conversion error at the checkout. When you place the order, round up to the nearest half-tonne or tonne the supplier delivers in, and ask about minimum load charges — a small job may pay the same for two tonnes as for one.

Bulk delivery by tipper truck is far cheaper per tonne than bagged aggregate for anything more than a wheelbarrow or two, but bags are convenient for small, precise quantities and for sites a truck cannot reach. If you are combining gravel with other work, the concrete slab calculator sizes the concrete that often sits on top of a compacted base, the excavation calculator works out the spoil you dig out to make room for the base, and the landscaping calculator helps with the wider garden takeoff.

Say you are building a gravel driveway 12 metres long and 3.5 metres wide, with a 150 millimetre compacted sub-base of road base and a 50 millimetre decorative gravel wearing layer on top. The area is 42 square metres. For the sub-base, 42 × 0.15 = 6.3 cubic metres of compacted volume; add 25 percent for compaction to get about 7.9 cubic metres loose, and at 1.9 tonnes per cubic metre that is roughly 15 tonnes of road base. For the top layer, 42 × 0.05 = 2.1 cubic metres; add 10 percent for spillage and at 1.6 tonnes per cubic metre that is about 3.7 tonnes of decorative gravel.

Run each layer through the calculator separately — different depth, different material, different allowance — and you end up with two clean order lines: about 15 tonnes of road base and about 3.7 tonnes of gravel. That is a far more reliable order than a single guessed 'twenty tonnes should do it', and it lets you price each material at its own rate. Break every gravel job into layers, size each layer as area times depth times density with the right allowance, and the deliveries arrive at the quantity you actually planned for.