Gravel size numbers are not marketing. They come from a standard published as AASHTO M43 and, almost identically, as ASTM D448, and each number defines how much material has to pass each sieve. A #57 has a 1 inch nominal top size and no fines; crusher run is everything from the top size down to dust; pea gravel is small, rounded and structurally useless. Which one you want depends entirely on whether you need the stone to drain or to lock up.
Where the numbers actually come from
Walk into any quarry in the United States and ask for a #57 and you will get something recognizably similar, whether you are in Oregon or Georgia. That is not an accident and it is not a trade convention. It is a published standard: AASHTO M43, Standard Specification for Sizes of Aggregate for Road and Bridge Construction, whose Table 1 lists the standard sizes of processed coarse aggregate. ASTM D448 covers the same ground for standard sizes of coarse aggregate for highway construction, with essentially the same size numbers.
State specifications call those tables up by name rather than reinventing them. Hawaii's Standard Specifications, to take one public example, simply require an aggregate size to fall "within limits shown in AASHTO M 43, Table 1 — Standard Sizes of Processed Coarse Aggregate". That is the whole mechanism: the standard defines the envelope, the state adopts it, the quarry produces to it, and the number on the invoice means something.
The gradation tables in AASHTO M43 and ASTM D448 are copyrighted and are not reproduced here. What follows describes what the size numbers mean and how to read them — for the actual percent-passing limits, buy the standard or look up the specification book your job is being built to, which will publish the numbers it enforces.
Two things are worth knowing about how the numbering works. First, a single-digit number is a narrow size range: a No. 4, a No. 5, a No. 8. Second, a two-digit number is a blend of two of them — a No. 57 spans what a No. 5 and a No. 7 cover between them, which is why it is wider than either. The same logic produces #67, #78 and #89. A number does not tell you the rock, the color or the hardness. It tells you the sieve sizes, and nothing else.
The distinction that matters most: clean or dense-graded
If you remember one thing from this page, make it this one. Every argument about gravel comes down to whether the fines were left in.
Clean, open-graded
Screened and often washed, so the dust is gone. The particles are all roughly the same size, which leaves large voids between them. Water runs straight through. It never binds, never forms a crust, and stays loose forever under a tire.
Examples: #57, #67, #8, #89. Jobs: french drains, septic fields, pipe bedding, structural backfill behind a wall, a gravel bed under a slab.
Dense-graded
Everything from the top size down to stone dust, left in. The fines fill the voids between the larger stones, so the material compacts to a hard, tight surface. It sheds water rather than passing it, which is exactly what a road wants.
Examples: crusher run, quarry process, ABC, dense-graded base, surface gravel. Jobs: driveway base and surface, road base, pad under a shed or a slab.
FHWA's Gravel Roads Construction & Maintenance Guide spends most of a section on why the fines matter, and the reason is not what people expect. Good surface gravel needs a percentage of plastic material, usually natural clay, "which will give the gravel a binding characteristic and hence a smooth driving surface". Without it, the guide says flatly, the material "will not form a crust to keep the material bound together". That is why a driveway of clean #57 goes on moving under your tires no matter how much of it you buy.
Base course and surface gravel are not the same product
Both are dense-graded, and people order the wrong one constantly. The FHWA guide sets the two side by side, using South Dakota's own specifications as the example, and the differences are specific.
| Requirement | Aggregate base course | Gravel surfacing |
|---|---|---|
| Top size | 100% passing 1 in; up to 20% retained on ¾ in | 100% passing ¾ in |
| Passing No. 4 | 46–70% | 50–78% |
| Passing No. 200 (the fines) | 3–12% | 4–15%, sometimes modified to 8–15% |
| Plasticity index | 0–6 | 4–12 |
Read the last two rows again. A base course can legitimately have a plasticity index of zero — no binder at all — because its job is structural strength under something else. A surface gravel must have at least 4, because its job is to bind into a crust you drive on. The guide's own comment on using base course as a surface is blunt: too much large stone, difficult blade maintenance, a rough driving surface. It will be good for one purpose or the other, but not for both.
The names you will actually be quoted
- #57 stone — the most widely sold clean stone in the country. Nominal 1 inch top size, washing out at the No. 4 sieve, almost no fines. Drainage, pipe bedding, structural backfill, under-slab. Not a driveway surface.
- #67 stone — a slightly smaller cousin, ¾ inch nominal, same clean character. Often used in concrete and where a #57 is too coarse.
- #8 and #89 — ½ inch nominal clean chips. Paver joints, permeable pavement, chip seal, choker over a coarser stone.
- Crusher run (also quarry process, QP, crush and run, ABC in the Carolinas, DGA in Kentucky) — dense-graded, top size down to dust. The default driveway and pad material. Compacts hard.
- Breaker run — coarse crushed rock straight off the primary crusher, larger than base. Bridging soft subgrade under a base course.
- Pea gravel — small rounded stone, around ⅜ inch, water-worn rather than crushed. Rounded and single-sized is the worst structural combination there is: the grains roll over each other instead of interlocking. Walkways, dog runs, decorative beds, playground surfacing. Never a base.
- Recycled: RAP and RCA — milled asphalt and crushed concrete, produced to base gradations. Both were measured in the WisDOT weight-volume study and both work as base; RCA has the widest and least predictable behavior of anything tested.
Your state may not use the AASHTO numbers at all. Indiana specifies a No. 53 and a No. 73; North Carolina sells ABC. Those are state designations with state gradations behind them, published in that state's own specification book. When a supplier quotes you a number, ask which specification it is written to — on a job with a contract, that book is the one that governs.
Same number, different weight
Here is the part that catches people ordering by the ton. The size number fixes the gradation. It does not fix the rock, and rock is what you are paying for by weight.
FHWA tested open-graded aggregates for use as structural backfill and measured the unit weight of its No. 57 samples between 95.4 and 108.7 lb per cubic foot — a 14% spread across material that all carried the same size number. The No. 8 samples in the same study ran from 85.7 to 112.8 lb/ft³. Granite, limestone and trap rock simply do not weigh the same, and the number on the ticket says nothing about which one is in the truck.
Compaction moves the figure again, and further. The WisDOT weight-volume study measured dense-graded ¾ inch base at 1.80 to 1.86 short tons per compacted cubic yard and found the same material expanding 36% to 47% going from compacted in place to a loose stockpile. A yard in the trench and a yard in the truck are two different quantities of stone. The tons are the same in both places, which is the whole argument for ordering by weight.
Run your own numbers with the gravel calculator, which carries the measured conversion and expansion factors per material, or lay out a driveway layer by layer with the gravel driveway depth calculator. To convert between the two units for any material, the cubic yards to tons converter shows the density it used and where it came from.
Bottom line
- The size numbers are real and standardized — AASHTO M43 and ASTM D448 — and they describe sieve sizes only, never the rock.
- Clean stone drains and never locks up. Dense-graded material with fines compacts into a crust. Pick by which behavior you need.
- #57 is the default clean stone; crusher run is the default dense-graded one. Putting #57 on a driveway surface is the most common expensive mistake in this whole subject.
- Base course and surface gravel are both dense-graded and still not interchangeable: a base can have zero plasticity, a surface needs at least 4 to bind.
- Two loads of #57 can differ 14% in weight because they are different rock. Order by the ton and take the density off your own delivery ticket.
- If a supplier's number is not an AASHTO one, it is a state one. Ask which specification, and build to that book.