Gravel, after it is compacted

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Gravel is sold by weight and used by volume

The unit mismatch is the whole problem. You calculate a hole in cubic yards. The yard sells you tons. Nobody publishes the conversion because it is not a constant — and the gap between the two is where people either run short on a Saturday or pay to haul away a pile.

Every quantity you can compute from a tape measure is a volume. Area times depth, converted to cubic yards. That is the number this calculator produces, and it is the only number the geometry can give you honestly.

Most aggregate suppliers, however, price and load by the ton, because a truck is weighed and a scale ticket is unambiguous in a way that a heaped bucket is not. So the last step of every gravel purchase is a conversion from cubic yards to tons — and that conversion is a property of the specific material, not of gravel in general.

Why there is no universal number. The tons in a cubic yard depend on the gradation (how the small stones pack into the gaps between the large ones), the parent rock (a granite and a limestone do not weigh the same), whether the stone is washed or has fines in it, and how wet the pile was when it was loaded. A screened single-size decorative stone and a dense-graded crusher run of the same nominal size are different products with different densities.

So ask, and get it in writing on the ticket. The one question that removes all of this: "how many tons per cubic yard for this specific product?" Every scale house knows the answer for the material in their own bins. It takes one phone call and it is the difference between ordering right and ordering twice. HyreYard does not sell aggregate and holds no density data, so we will not invent a figure to fill this gap — the supplier’s number for their own stone is better than any national average could be.

The second trap is the delivery minimum. Bulk aggregate is usually sold in truck loads with a minimum, and the haul is often a flat charge rather than a per-ton one. That means small jobs have a cost floor that has nothing to do with the volume you calculated, and it is frequently cheaper per unit to take slightly more in one load than to make two trips.

The disclosure

Why the delivered pile looks like too much

The pile is not too much. Loose delivered volume and compacted in-place volume are different quantities, and the difference is the point of the exercise — a base that has not lost volume has not been compacted, and a base that has not been compacted will settle under the thing you build on it.

Compaction is a real, measurable, specified thing. ICPI Tech Spec 2 — Construction of Interlocking Concrete Pavements requires bases for pedestrian areas and residential driveways to be compacted to a minimum 98% of standard Proctor density, ASTM D698. For vehicular areas the requirement rises to 98% of modified Proctor density, ASTM D1557 or AASHTO T180. Those are density targets measured with a nuclear density gauge or an approved equivalent, not "run over it with the plate a few times".

It is done in lifts. The same document says to spread and compact the base in 4 to 6 in lifts using 7,000 lbf (31 kN) reversible plate compactors, and that thinner lifts are required for lighter machines. This is the single most common corner cut on a DIY base: dumping eight inches of stone and compacting the top two. The surface passes the boot test and the bottom four inches are still loose, which is exactly where the settlement comes from a year later.

Our ×1.2 allowance is editorial and we say so every time. Compaction is a real volume change and ICPI requires the base to reach 98% of standard Proctor density. The ratio between the loose volume you buy and the compacted volume you end up with depends on gradation, moisture and the compactor, and there is no published national figure for "crushed stone". Twenty percent is our planning allowance, not a measurement of your quarry.

Turn the allowance off when it does not apply. Decorative stone in a bed is not being compacted. Drainage stone wrapped in geotextile behind a wall is deliberately not being compacted to a density target, because you want the voids. A pre-compacted recycled product may already have been processed. In all of those cases the geometry alone is the answer and the multiplier is wrong.

Gravel is not a drainage solution by itself

A very common and expensive misunderstanding: putting stone where water collects does not remove the water. It gives the water somewhere to sit that you can no longer see.

Stone stores water; it does not transport it. An open-graded stone is roughly a third voids, so a cubic yard holds meaningful water — but it only moves if there is somewhere for it to go, downhill, with an outlet. A gravel trench with no outlet is a buried bathtub. It will hold water for a while, then fill, then the surface will be wet again and you will have spent the money.

The outlet is the design. Where does the water leave? Daylight on a slope, a storm connection where one is permitted, a dry well sized to the soil’s infiltration rate. If none of those exists, no amount of stone changes the outcome, and the correct first move is grading and downspout extension rather than excavation.

And the surface you build may be the cause. The EPA notes that in developed areas "much of the land surface is covered by buildings, pavement and compacted landscapes. These surfaces do not allow rain and snow melt to soak into the ground which greatly increases the volume and velocity of stormwater runoff". A new patio is a new impervious surface. The water that used to soak in where it fell now arrives somewhere else, at a higher rate, and where it arrives is a design decision you are making whether or not you think about it. The EPA page states the mechanism and does not publish a runoff percentage. We do not publish one either.

Which is why the soil lookup comes first. The NRCS hydrologic soil groups are a direct statement about how much of the rain will run off rather than soak in. Group A is deep sand and takes water readily; Group D is high-shrink-swell clay, a claypan or shallow soil over rock and sheds nearly all of it. Building the same detail on both is how one of them fails.