Gravel Calculator

Cubic Yards, Tons, and Why Suppliers Quote Both

Gravel is one of the few materials sold two different ways at the same yard. Volume, in cubic yards, is what fills the space being measured. Weight, in tons, is what goes across the scale and onto the ticket. Both describe the same pile, and the conversion between them depends entirely on what kind of stone is in it.

The reason for the split is practical. Trucks are weighed, so tons are exact and easy to bill. Projects are measured in length, width and depth, so cubic yards are what an estimate naturally produces. Any gravel order therefore starts as a volume and gets converted to weight at the last step.

The density problem

There is no single conversion from cubic yards to tons, because a yard of small angular crushed stone packs tighter than a yard of large rounded river rock. The useful working figures are about 1.4 tons per cubic yard for crushed stone, about 1.35 for pea gravel and about 1.3 for river rock. Crusher run, which contains stone dust that fills the gaps between the larger pieces, runs heavier at roughly 1.5 tons per cubic yard.

Moisture shifts these numbers. Stone that has sat through a week of rain weighs noticeably more per cubic yard than the same stone dry, which is why a load that looks small on the pile can still hit the ticketed tonnage. When precision matters, ask the supplier for the density of the specific product, since local rock type varies.

A Worked Example: A 40 ft by 12 ft Driveway at 4 Inches

Take a driveway 40 feet long and 12 feet wide, topped with 4 inches of crushed stone.

• Convert depth: 4 divided by 12 equals 0.3333 feet.
• Volume: 40 x 12 x 0.3333 equals 160 cubic feet.
• Cubic yards: 160 divided by 27 equals 5.93 cubic yards.
• Add 10 percent waste: 5.93 x 1.10 equals 6.52 cubic yards.
• Convert to tons at 1.4 tons per cubic yard: 6.52 x 1.4 equals 9.13 tons.

So the order is about 6.5 cubic yards or about 9.1 tons of the same material. If the supplier sells by the ton, ask for 9.1 tons. If they sell by the yard, ask for 6.5. Ordering 6.5 tons because the calculator said 6.5 cubic yards is a mistake that leaves the job roughly 30 percent short.

How Deep Should the Gravel Be?

• 2 to 3 inches: decorative beds, borders and areas around plantings. Deep enough to cover soil and suppress light weed growth, shallow enough not to smother roots.
• 4 inches: garden walkways and foot paths. Enough to stay put underfoot without becoming loose and hard to walk on.
• 4 to 6 inches: compacted base under pavers, flagstone or a patio. This is structural, not decorative, and it should be compacted in lifts.
• 6 to 8 inches: a vehicle driveway, built in two layers rather than one deep dump of a single material.

Deeper is not automatically better. Loose gravel over about 4 inches deep in a walking area gets soft underfoot and migrates. Depth for traffic areas belongs in the compacted base, not in the loose surface layer.

Compaction and the 20 Percent Rule

Gravel delivered loose is full of air. Once it is spread, wetted and compacted with a plate compactor or driven over for a few weeks, it settles significantly. Angular crushed stone with fines can lose roughly 20 percent of its loose volume during compaction. That is why a bed that measures 4 inches deep after compaction needs closer to 5 inches of loose material going in.

In ordering terms, roughly 20 percent more than the finished depth suggests is the practical allowance for anything that will be compacted, which is on top of any waste allowance for spillage and uneven subgrade. For purely decorative gravel that will never be compacted, a 5 to 10 percent allowance for spread and settling is enough.

Building a Gravel Driveway in Layers

A driveway that lasts is not one material at one depth. It is a coarse base that carries load and a finer top that drives and looks well.

• Base layer: 4 inches of crusher run, also sold as quarry process, ABC or dense grade aggregate. It contains stone dust that locks the aggregate together when compacted, so it behaves almost like a soft pavement.
• Top layer: 2 to 4 inches of a cleaner decorative stone, often 3/4 inch crushed stone or river rock, spread over the compacted base.

Compact the base before adding the top, and compact in lifts of no more than 3 to 4 inches. A single 8 inch dump compacted from the top leaves the lower half loose, which is where ruts begin. On soft ground, expect the first few inches of base to be pressed into the subgrade and effectively lost, and order accordingly.

Gravel Types and What Each One Is For

Rounded stone such as pea gravel and river rock never locks together, so it stays loose and rolls underfoot or under tires. It is a decorative and drainage material, not a base. Angular crushed stone interlocks when compacted and is what belongs under anything structural.

Bagged or Bulk?

Bagged gravel at home centers is usually sold in 0.5 cubic foot bags, which means 54 bags to a cubic yard. For the 6.5 cubic yard driveway above, that is over 350 bags, which is not a serious option. Bags make sense for small repairs, container drainage, a single planting bed or anywhere a truck cannot reach.

Bulk wins on cost per cubic foot at almost any real project size, typically once the job passes roughly a third of a cubic yard. The variables are delivery fee, minimum load and whether the truck can dump where the gravel is needed. Hauling bulk in a pickup is limited by weight, not space: a half ton pickup is at its legal limit well under one cubic yard of crushed stone, since a single yard weighs about 2,800 pounds.

Drainage and Geotextile Fabric

Gravel over bare soil does not stay gravel for long. Soil migrates up into the voids, the layer loses drainage capacity, and weeds take root in the mixed material. A non woven geotextile fabric laid between the subgrade and the stone separates the two and keeps the gravel layer working as designed. It also spreads load, which reduces rutting on soft ground.

Landscape fabric sold for weed control is not the same product. It is thinner, tears under aggregate and vehicle loads, and is not designed as a separation layer. For driveways and paver bases, use a proper woven or non woven geotextile.

For drainage trenches and French drains, use washed stone with the fines removed. Crusher run in a drain trench does the opposite of what is wanted, because the dust that makes it compact so well also blocks water movement.

Costly Mistakes to Avoid

1. Ordering tons when the calculation produced cubic yards, which leaves the job around 30 percent short.
2. Multiplying by depth in inches instead of converting to feet first.
3. Skipping the compaction allowance, then finding the finished surface an inch below the intended grade.
4. Using rounded stone such as pea gravel or river rock as a driveway base, where it will never lock together.
5. Dumping the full depth in one lift instead of compacting in 3 to 4 inch layers.
6. Putting decorative stone straight onto soil with no geotextile separation.
7. Using crusher run in a French drain, where the stone dust blocks drainage.
8. Buying bagged gravel for a bulk sized job, at several times the price per cubic foot.
9. Overloading a pickup, since one cubic yard of crushed stone weighs about 2,800 pounds.
10. Assuming a single density figure for every product, when crusher run and river rock differ by roughly 15 percent per cubic yard.