Gravel Calculator

What the gravel calculator does

Gravel is sold by weight, but you measure your project by area, so somewhere in the middle a conversion has to happen. This does it. You give it the shape and depth of the area you are filling, and it returns the volume in your choice of units and the weight in tonnes, plus a cost if you add a price.

It also lets you set the density of your particular gravel, since not all gravel weighs the same. Below is how it gets from a patch of ground to a number you can hand a supplier.

How to use it

1. Pick the shape. Rectangular for a driveway or pad, circular for a fire pit base or a round bed.
2. Enter the dimensions and the depth. Each with its own unit, and you can mix them freely.
3. Set the density. The box starts at a typical gravel density, around 1,680 kg per cubic metre. Change it if your supplier gives you a different figure.
4. Add a price per tonne if you want a cost, pick your output unit, then press Calculate, or Reset to clear it.

How the volume and weight are worked out

The volume is just the area of the ground times how deep you want the gravel:

Volume = area × depth

For a rectangle the area is length times width, and for a circle it is pi times the radius squared. Then the weight comes from the volume and the density, since density is simply how heavy the material is for its size:

Weight = volume × density

That is why the density box matters. Gravel is sold by the tonne, so getting the weight right is what lets you order the correct amount, and a heavier or lighter gravel changes that weight for the same hole.

How far a cubic yard of gravel goes

It helps to picture how much ground a yard covers, and since this is pure geometry it is the same for any loose material. A cubic yard is 27 cubic feet, so spread thinner it covers more ground, spread deeper it covers less.

So a cubic yard is roughly a pickup load, or about nine full wheelbarrows, which is a useful gut check before a delivery turns up.

How deep to lay gravel

The depth you choose is what drives the whole estimate, so it is worth getting right for the job. A decorative layer over a path or bed is usually fine at 2 to 3 inches. A driveway or anything that carries vehicles wants more, around 4 to 6 inches, and is often laid in layers over a compacted sub-base rather than as one deep pour.

For a driveway, a coarser stone underneath with a finer gravel on top tends to hold up better than a single grade, so you may be ordering two depths for the same area.

A worked example: a 20 ft by 10 ft pad

Say you are laying gravel on a 20 foot by 10 foot pad, 4 inches deep, using a typical gravel.

The area is 20 × 10 = 200 square feet, and at 4 inches (0.33 ft) deep that is 200 × 0.33 = about 66.7 cubic feet, which is 2.47 cubic yards. At a typical density that comes to roughly 3.2 tonnes.

So you would order in the region of 3.2 tonnes, then add a little for the reason in the next section.

Ordering, and a note on compaction

Order a bit more than the bare figure, usually 10 to 15 percent, to cover uneven ground, settling, and the spread that happens when gravel is raked out. Coming up a little short on the last stretch of a path is a frustrating reason for a second trip.

One thing specific to gravel: if you are compacting it, for a driveway or a road base, it packs down as you roll it, so the loose volume you order ends up shallower once it is settled. Some gravels lose a noticeable share of their loose volume to compaction, so for a compacted job lean toward the higher end of that margin.

Questions people ask

How much gravel do I need?

Work out the area, multiply by the depth for the volume, then multiply by the density for the weight. A 200 square foot pad at 4 inches deep needs about 2.47 cubic yards, or roughly 3.2 tonnes.

How many tonnes are in a cubic yard of gravel?

Most gravel runs about 1.4 to 1.7 tonnes per cubic yard, depending on the stone and how wet it is. Heavier stone sits at the top of that range.

How much area does a yard of gravel cover?

About 108 square feet at 3 inches deep, or 81 square feet at 4 inches. The thinner you spread it, the more ground it covers.

How deep should gravel be for a driveway?

Around 4 to 6 inches, usually laid in layers over a compacted base, rather than 2 to 3 inches for a decorative path.

References

A quick note on where these figures come from. The coverage numbers are pure geometry, just the 27 cubic feet in a cubic yard spread over an area at a given depth. The way a material's bulk density is measured, which is what turns volume into weight, follows the ASTM test standard for the density of aggregate. The unit conversions follow the US National Institute of Standards and Technology guide.

1. ASTM C29/C29M, Standard Test Method for Bulk Density (Unit Weight) and Voids in Aggregate. https://www.astm.org/c0029_c0029m-23.html
2. National Institute of Standards and Technology (NIST), Special Publication 811, Guide for the Use of the International System of Units (SI). https://www.nist.gov/pml/special-publication-811