How much gravel do I need?

Volume first, weight second

Gravel is ordered in two different ways, and mixing them up is the most common way to end up with the wrong amount. Some suppliers sell by volume (cubic yards in the US, cubic meters elsewhere). Others sell by weight (tons in the US, tonnes elsewhere). Every gravel estimate starts with volume, because volume is the thing you can measure with a tape. Weight is then a conversion that depends on how dense the stone is.

Volume is the area you are covering times the depth. In US units, measure length and width in feet, but think about depth in inches, since nobody says they want a 0.33 foot layer. Divide the inches by 12 to get feet, multiply the three numbers to get cubic feet, then divide by 27 to get cubic yards, because a cubic yard is 3 ft x 3 ft x 3 ft.

To get from yards to tons, multiply by a density. EveryFix's Gravel Calculator and Gravel Driveway Calculator both use 1.4 tons per cubic yard for standard crushed gravel. In metric mode they report tonnes, which is the same 1.4 US tons per cubic yard converted to metric units.

The formula

Cubic feet = length (ft) x width (ft) x depth (in) / 12. Cubic yards = cubic feet / 27. Tons = cubic yards x 1.4.

In metric, volume in cubic meters is length (m) x width (m) x depth (m), with centimeters divided by 100 first. One cubic yard is 0.7646 cubic meters, so one cubic meter is about 1.308 cubic yards.

The 1.4 figure is an assumption, not a law. It is a typical value for crushed gravel, and the weight you actually receive depends on the stone type, how much fine material is mixed in, and how wet the pile is. Treat the tons figure as a planning number and let your supplier confirm their own conversion.

Choosing a depth by use

Depth is the input that moves the answer most, and it depends on what the gravel has to do. Doubling the depth doubles the volume and the weight, so a wrong guess here costs far more than a rounding error elsewhere.

A decorative layer, a garden path, or a drainage bed that only foot traffic touches is a thin job. The Gravel Calculator starts at 2 inches (5 cm in metric) for that kind of work, and a thin layer on a path is common. A driveway is a different job, because the stone has to carry vehicles. The Gravel Driveway Calculator starts at 4 inches (10 cm in metric) for a crushed gravel base, and the calculator notes that heavier traffic areas may need more. Soft soil, steep slopes, and heavy vehicles all push the depth up.

This guide covers the arithmetic, not the structural design. For a driveway that will carry loaded trucks or support a retaining edge, check local requirements and ask the supplier or a local contractor what depth and stone grading suits your ground. Then put that depth into the calculator.

• Garden path or decorative bed: thin, often around 2 to 3 inches
• Drainage bed or trench: depends on the design, so measure the actual trench
• Driveway base: the Gravel Driveway Calculator starts at 4 inches, with more for heavy use
• Built-up driveway with a base and a top layer: calculate each layer separately

Worked example: a garden path

Say you want a path 30 ft long and 3 ft wide with 2 inches of gravel. The area is 30 x 3 = 90 sq ft. The depth in feet is 2 / 12 = 0.167 ft, so the volume is 90 x 2 / 12 = 15 cubic feet.

Cubic yards: 15 / 27 = 0.56. Tons: 0.56 x 1.4 = 0.78 tons, or about 1,556 lb. That is a small order, and many garden centers sell gravel in bags or by the scoop at that scale, so convert the cubic feet into whatever unit the bag is sold in rather than rounding the order to a full yard.

Metric version: a path 8 m long and 1 m wide with 5 cm of gravel is 8 x 1 x 0.05 = 0.4 cubic meters. At about 1.66 tonnes per cubic meter (the metric equivalent of 1.4 US tons per cubic yard), that is roughly 0.66 tonnes.

• Area: 30 x 3 = 90 sq ft
• Volume: 90 x 2 / 12 = 15 cu ft
• Cubic yards: 15 / 27 = 0.56
• Weight: 0.56 x 1.4 = 0.78 tons
• Metric path: 8 x 1 x 0.05 = 0.4 cubic meters, about 0.66 tonnes

Worked example: a driveway base

Now a driveway 40 ft long and 12 ft wide. At 4 inches deep, the volume is 40 x 12 x 4 / 12 = 160 cubic feet. That is 160 / 27 = 5.93 cubic yards, and 5.93 x 1.4 = 8.30 tons.

Depth matters a lot here. At 6 inches the same driveway is 240 cubic feet, 8.89 cubic yards, and 12.44 tons. At 8 inches it is 320 cubic feet, 11.85 cubic yards, and 16.59 tons. Going from 4 to 8 inches doubles the order, which is why it is worth settling on the depth before you call a supplier.

Metric version: a drive 10 m long and 3.5 m wide at 10 cm deep is 10 x 3.5 x 0.10 = 3.5 cubic meters, about 4.58 cubic yards. At about 1.66 tonnes per cubic meter that is roughly 5.81 tonnes. At 15 cm the volume rises to 5.25 cubic meters and about 8.72 tonnes.

• 4 in deep: 160 cu ft, 5.93 cu yd, 8.30 tons
• 6 in deep: 240 cu ft, 8.89 cu yd, 12.44 tons
• 8 in deep: 320 cu ft, 11.85 cu yd, 16.59 tons
• Metric 10 cm: 3.5 cubic meters, about 5.81 tonnes
• Metric 15 cm: 5.25 cubic meters, about 8.72 tonnes

Compaction: why you order more than the math says

The calculators treat your area as a uniform block of loose stone at full depth. Real gravel does not stay that way. Once you rake, drive on it, or run a plate compactor over it, the stone settles into itself and the layer gets thinner. A common planning rule is that gravel compacts by roughly 10 to 20 percent, so a layer you spread to 4 inches loose may finish noticeably thinner.

There are two ways to deal with that. You can order extra, or you can spread in layers and compact each one, which gives a firmer result anyway. Either way, build the margin into the order. On the 5.93 cubic yard driveway, a 10 percent margin is 6.52 cubic yards (9.13 tons) and a 20 percent margin is 7.11 cubic yards (9.96 tons).

If you are building a base course plus a separate top-dressing layer, run the calculator once for each layer and depth, then add the two results. Do not average the depths into one number, because the layers usually use different stone sizes that you buy separately.

Tons versus cubic yards, and why density changes the answer

A supplier may quote by the ton, by the yard, or both. If the price is per ton and the pile is dense crushed stone, a cubic yard weighs more than it would for lighter round stone like pea gravel. The 1.4 tons per cubic yard figure sits in the middle. The Gravel Driveway Calculator notes that denser angular crusher run can run closer to 1.5 tons per cubic yard, while rounder gravel or river rock is often lighter, closer to 1.2 to 1.3.

On the 5.93 cubic yard driveway, that spread matters. At 1.2 tons per cubic yard you need 7.11 tons. At 1.3 it is 7.70, at 1.4 it is 8.30, and at 1.5 it is 8.89. The volume is identical in every case, and the weight changes by almost two tons. If your supplier sells by weight, ask for their tons-per-yard figure for the exact product and substitute it.

Also watch which ton you mean. A US ton is 2,000 lb. A metric tonne is 1,000 kg, about 2,205 lb, so the two are not interchangeable. Using a tonne figure with a US-ton price, or the reverse, is an easy way to be off by roughly 10 percent.

Common mistakes

A few errors account for most over- and under-orders.

• Leaving depth in inches while length and width are in feet, which inflates the volume by a factor of 12.
• Ordering to the exact calculated number with no margin for compaction, uneven ground, or spillage.
• Treating the tons estimate as fixed when the stone type changes the weight per yard.
• Mixing US tons and metric tonnes between your estimate and the supplier's quote.
• Using one blended depth for a driveway that has a base layer and a top layer of different stone.