Gravel Calculator

How to estimate gravel

Gravel splits into two very different problems. Working out the volume is exact arithmetic. Converting that volume into tons is an estimate, and no calculator on the internet can make it exact, including this one. It is worth understanding why before you order.

cubic feet = area (sq ft) × depth (in) ÷ 12
cubic yards = cubic feet ÷ 27
tons = cubic yards × density (tons per cu yd)The first two lines are geometry and are exact. The third depends on the specific stone.

The volume part is exact

Area times depth, with the depth converted from inches to feet, then divided by 27 to get cubic yards. A 40 by 10 foot driveway at 4 inches is 400 square feet times 0.333 feet, which is 133 cubic feet, or 4.94 cubic yards.

Nothing about that is negotiable. If a supplier quotes you a different cubic yardage for the same dimensions, one of you has made an arithmetic error.

The tonnage part is not

Here is the honest bit. Suppliers usually sell gravel by weight, but weight per cubic yard is a property of the material, not a constant. Crushed stone commonly runs around 1.3 to 1.5 tons per cubic yard. Dense crusher run, which mixes stone with stone dust to compact tightly, sits near the top of that band. Granite is heavier than limestone. Wet stone weighs more than the same stone dry.

That spread is over 20 percent from end to end, which is far bigger than any rounding decision you will make elsewhere in the estimate. This calculator defaults to 1.4 tons per cubic yard and puts the field in front of you rather than burying it, because the right move is to call your supplier, ask what their material weighs per yard, and type that number in.

Order in cubic yards where you can. It is the number you can defend. If they only sell by the ton, get their density and convert with it rather than ours.

How deep

Depth follows the load. Two inches is a top dressing refreshing an existing surface. Three inches works for garden paths and decorative beds where nothing heavier than a wheelbarrow crosses. Four inches is a normal driveway layer over an established base. Six inches or more is base course under pavers, or a driveway that carries trucks.

Anything at base-course depth should go down in compacted lifts rather than one deep pour. Two 3 inch lifts, each compacted, behave very differently from 6 inches dumped and raked.

Compaction changes the number

If the gravel will be compacted or driven on, the finished depth is less than the loose depth you spread. That means a compacted 4 inch layer needs more than 4 inches of loose material to start with.

Adding 10 to 15 percent over the calculated volume is normal for base course. For decorative gravel that nobody drives on, the calculated volume is enough. This calculator gives you the finished volume, so add the compaction margin yourself if the job calls for it.

What one cubic yard covers

Handy for checking a quote against your yard. One cubic yard spreads to about 160 square feet at 2 inches, 108 at 3 inches, 81 at 4 inches, and 54 at 6 inches. It is the same division run backwards: 27 cubic feet divided by the depth in feet.

So a single yard does a 10 by 8 foot pad at driveway depth. If your area is much bigger than that, you are ordering by the truckload rather than by the bag, and the density question above starts to matter in real money.

A quick cost check

Take that 40 by 10 driveway at 4 inches: 4.94 cubic yards, about 6.9 tons at 1.4. At $45 a delivered ton that is roughly $310. At 1.3 tons per yard it is 6.4 tons and about $290. At 1.5 it is 7.4 tons and $335. Same hole, same stone volume, $45 of spread purely from the density assumption. That is why the field is editable.

Common estimating mistakes

• Trusting a tonnage you did not source. The volume is the reliable number. Tonnage is only as good as the density behind it.
• Forgetting to divide by 12. Depth is in inches and everything else is in feet.
• Ignoring compaction on a base course. Spread depth and finished depth are not the same thing once a compactor has been over it.
• Skipping the fabric. Gravel laid straight onto soil sinks into it, and within a couple of seasons you are buying part of the same order again.
• Underestimating the handling. Nearly 7 tons dumped at the end of a driveway is a lot of wheelbarrow trips.

When to call someone

Drainage is the honest boundary. Gravel changes where water goes, and a new driveway or pad that redirects runoff toward a foundation, a neighbor's yard, or a septic field is a real problem that a volume calculation cannot warn you about. If the ground slopes toward a building, get someone to look at it first.

The other one is scale. Past about 10 tons you are into machine work, and hand-spreading stops being reasonable.