Gravel and Stone Sizes Explained

Ask five contractors what "57 stone" is and you may get five slightly different answers. One calls it "three-quarter clean," another says it is "one-inch down to dust," and a third insists it drains. The confusion is not their fault. Aggregate size numbers are not measurements — they name a gradation, a permitted percentage of material passing each of a series of sieves, and the same number can behave very differently depending on how much dust the producer leaves in the load. This guide explains what the numbers actually mean, how to translate them into plain language, and how to pick the right stone for a driveway, a drainage bed, a slab base, or a retaining wall.

Why the Numbers Confuse Everyone

A number like "57" is not shorthand for five-eighths or seven-sixteenths of anything. It is a size class from a standard gradation system, the same way "2x4" is a lumber class rather than a literal measurement. The number refers to a defined envelope of particle sizes and to how much of the load is allowed to pass each sieve, not to a single dimension you can eyeball on the pile.

That is why a supplier's plain-language shelf tag often disagrees with the formal specification. A yard may sell "#57" that looks a little chunkier or dustier than the #57 the engineer specified, and both can be technically defensible within the allowed tolerances. When the stone actually matters — structural base, drainage, concrete — the printed gradation chart is worth far more than the eyeball test.

What an Aggregate Size Number Actually Means

The numbered system most U.S. contractors use traces back to AASHTO M 43 and ASTM C33 / ASTM D448, which defines aggregate size numbers and their standard size ranges. State departments of transportation publish their own gradation tables that closely mirror these national standards, with regional variations in tolerances and naming.

Every size class is pinned down by four things:

• Top size — the largest sieve that essentially all of the material passes.
• Bottom size — the smallest sieve the bulk of the material is retained on.
• Gradation curve — the percentage of the load that passes each intermediate sieve.
• Fines content — how much of the material passes the No. 200 (0.075 mm) sieve.

Two grades that look similar at a glance can behave very differently. #57 and #67 stone share a top size near three-quarters to one inch, but #67 has a tighter spread and compacts denser. That single difference is one of the most common decision points for slab base and driveway work.

Sieve Sizes in Plain English

Sieves are the screens the material is graded through, and a few numbers cover nearly every conversation you will have. The 1-inch sieve is 25 mm; the 3/4-inch sieve is 19 mm; the 3/8-inch sieve is 9.5 mm. The No. 4 sieve is 4.75 mm — roughly the size of a pencil eraser — and it is the practical dividing line between gravel-sized particles and sand-sized ones.

The No. 8 sieve is 2.36 mm, about a coffee bean. The No. 200 sieve, at 0.075 mm, is invisible to the naked eye; it is the "dust" that decides whether a material drains or seals. When someone says a stone is "clean," they mean it has very little material passing No. 200. When they say it is "dirty" or "has fines," they mean the opposite.

Open-Graded vs. Dense-Graded: The Distinction That Matters Most

Forget the decorative names for a moment. Almost every aggregate decision comes down to one question: do you want the layer to drain, or do you want it to lock up tight and carry load?

Open-graded aggregate has had most of its fines screened out. The material runs from a nominal top size down to about the No. 4 sieve with the smaller fractions removed, so the voids stay open and water flows through aggressively. Clean #57, #67, and #3 or #5 base stone are the classic examples. Use them where drainage is the priority: drainage beds, retaining wall backfill, and hydrostatic relief layers.

Dense-graded aggregate includes a continuous gradation from the top size all the way down through stone dust. Under a roller or plate compactor the fines fill the voids, the layer densifies, and it becomes a tight, smooth-rolling surface that sheds water laterally. Crusher run and other dense-grade base products are the examples. Use them where you need a firm, compactable base that resists rutting under traffic.

Both behaviors are useful, and both are wrong for some jobs. Treating the two as interchangeable is how driveways pump, rut, and migrate within a season.

The Sizes You Will Order Most Often

A handful of ASTM D448 size numbers cover the vast majority of site, driveway, drainage, and hardscape work. The ranges below are nominal — always confirm the exact gradation envelope with your supplier or the project specification.

• No. 2 (about 2 1/2" to 1 1/2") — large, stable subbase stone; high water storage capacity for permeable pavement and heavy-load pads.
• No. 3 (about 2" to 1") and No. 4 (about 1 1/2" to 3/4") — coarse drainage and heavy-duty base layers.
• No. 5 (about 1" to 1/2") and No. 56 (about 1" to 3/8") — road base and general drainage stone.
• No. 57 (1" down to the No. 4 sieve) — the workhorse: French drains, foundation drainage, septic drain fields, retaining wall backfill, and permeable base.
• No. 67 (about 3/4" down to the No. 4 sieve) — tighter than #57; common as concrete aggregate and a dense slab base.
• No. 8 (3/8" down to the No. 8 sieve) — paver bedding, exposed aggregate, and pervious concrete.
• No. 89 (3/8" down to the No. 16 sieve) and No. 9 (No. 4 to No. 16) — surface and mix aggregates.
• No. 10 (No. 4 down to zero) — stone dust or screenings; a compactable leveling course.

The key point for #57 is easy to miss: the standard allows 95 to 100 percent to pass the 1-inch sieve, but as much as 25 to 60 percent can pass the 1/2-inch sieve. A "one-inch" stone can therefore be mostly half-inch material. That is why depth and drainage behavior vary from load to load even when the number on the ticket stays the same.

What "Crusher Run" and "Dense-Grade" Really Mean

Crusher run is the umbrella term for any dense-graded aggregate produced by running quarried rock or concrete demolition material straight through a primary crusher with no clean screening step. Every fraction, from the largest particle down through stone dust, stays in the load. Typical North American crusher run runs from a three-quarters-inch to one-and-a-quarter-inch top size (some heavy-base products go to two inches), with a continuous gradation and roughly 5 to 15 percent passing the No. 200 sieve. That dust is the binder that locks the surface up under compaction.

Because crusher run is a regional product, the names change with the map even when the material does not. You will hear it called DGA (dense-graded aggregate) or DGABC in the Northeast, ABC (aggregate base course) in the Southeast, GAB in many DOT specifications, Item 4 in New York (NYSDOT Type 2 subbase), and 411, 21AA, 21A, or 2A modified in Pennsylvania, Michigan, and neighboring states. "Quarry process" or Q.P. is the older Northeast term still used colloquially. The same is true for crushed concrete, which is covered in its own guide to crushed concrete as a driveway base.

Matching the Stone to the Job

Once you understand open versus dense, specifying gets straightforward. For a drainage bed, a French drain, or a septic drain field, you want clean open-graded stone — #57 or #67 — so water moves freely without clogging. Do not use pea gravel or small rounded stone; it can compact and choke the void space the system depends on.

For a driveway, use dense-graded crusher run where the section needs to compact tight and resist rutting, and clean #57 where you need drainage, a choke layer above a coarse storage stone, or backfill along the edge. The strongest driveway sections use both, in different layers, doing different jobs — the same principle that drives the layered build in our guide to building a gravel driveway. For permeable pavement, a common stack is #2 stone in the storage layer, #57 as the choker, and #8 as the bedding under the pavers.

Behind a retaining wall, clean stone is not optional. Water that reaches the wall has to drain down through the stone and out through weep holes or a drainage pipe; crusher run or compacted soil placed directly against the wall traps water and is one of the most common causes of wall failure. The same logic applies to excavating and backfilling a retaining wall. Under a slab, base choice again comes down to drain versus lock up, which is why the base material matters as much as the excavation depth in our guide to preparing a site for a concrete slab.

Crushed Stone, Natural Gravel, and Recycled Concrete Are Not the Same

Crushed stone is manufactured: rock is blasted or excavated, fed through a crusher, and screened into controlled size fractions. The angular faces and sharp edges interlock under compaction, distribute load efficiently, and resist shifting under traffic. That angularity is the reason crushed products outperform rounded stone as structural base.

Natural gravel — river, bank-run, or glacial — formed as water and ice rounded the edges off rock over geologic time. It looks better and is comfortable underfoot, but rounded particles want to roll and migrate under load unless tightly contained by edging or structure. It is a fine choice for decorative paths and garden beds, and a poor choice for a primary structural base.

Recycled concrete aggregate (RCA) behaves much like virgin crushed stone in most base, drainage, and backfill applications, which is why it has become mainstream on site work.

How Much Stone to Order

Stone is ordered by volume — cubic yards — and sometimes by weight, so you need to convert the area you are covering into a volume. One cubic yard is 27 cubic feet, and coverage depends entirely on how deep you place it: one yard covers roughly 100 square feet at a 3-inch depth, about 80 square feet at 4 inches, and about 54 square feet at 6 inches.

Multiply length by width by depth (all in feet), divide by 27, and you have your base yardage. Then add 10 to 15 percent for compaction and waste, and confirm the density with your supplier if you are buying by the ton. A cubic yard of crushed stone runs in the neighborhood of 1.2 to 1.5 tons depending on material and moisture, which is the same range covered in our breakdown of how much a yard of dirt weighs. If you are trying to picture how many deliveries that is, see how many yards a dump truck holds.

Common Mistakes That Cost Money

The most expensive mistake is using an open-graded stone where a dense-graded base belongs, or the reverse. Clean #57 will not compact into a structural base — it has too much void space — and crusher run will not drain a wet site. Getting this backwards means the work fails and gets redone.

Placing stone in lifts that are too thick is the second costly habit. Thin, uniform lifts compact far better than one deep dump, and the material has to be the right moisture to lock up. Match the machine to the material and the layer thickness with our guide to choosing the right compaction equipment, and never compact over a soft, wet subgrade without first stabilizing it.

Finally, do not skip the separation layer on soft ground. A geotextile fabric keeps fine subgrade soil from pumping up into the stone and destroying the drainage and the base at the same time. Between correct gradation, correct lift thickness, and a fabric where it belongs, most aggregate failures are preventable before the first load is dumped.