Gravel Names Explained: What No. 57 Means and Why “Crusher Run” Varies

Some gravel names are numbers, such as No. 57, and a numbered size has a published range of stone sizes. A name such as crusher run is different: none of the three sources checked for this guide defines it, and the same goes for pea gravel and #411, which this guide does not cover. So for a numbered size you can look up what you are getting; for a name like crusher run, ask the supplier.

What the numbers mean

Penn State’s Center for Dirt & Gravel Roads Studies explains the numbering. It says AASHTO labels aggregate specifications from 1 to 10 according to the largest stone size in the mixture, with 1 the largest and 10 the smallest. Multi-digit numbers are blends: it gives AASHTO 57 as a blend of AASHTO 5 and AASHTO 7.

A Federal Highway Administration research report on aggregates for structural backfill reproduces the AASHTO M43 gradations for twelve of these sizes, in a table headed “Selected AASHTO M43-05 (ASTM D448) aggregate designations.”

Penn State adds that the AASHTO specifications are technically open-graded, or clean, aggregates. That word matters for the next two sections.

No. 57: a clean stone that drains

The FHWA report’s table gives the gradation for No. 57 as the percent of the stone that passes each sieve:

Sieve	Percent passing, No. 57
1.5 inches	100
1 inch	95 to 100
0.50 inches	25 to 60
No. 4	0 to 10
No. 8	0 to 5

Read from the top, nearly all of it is smaller than 1 inch, and from the bottom, almost none of it is fine. Penn State’s table describes #57 the same way in one line: 1.5 inches to 3/32 inch, clean.

Penn State says open-graded, clean aggregates have notable air voids between the stones and little to no fines, and that these mixtures drain effectively but do not compact well to form a dense mass. It lists base material and subsurface drainage as their road uses.

Why a mix with fines packs down

Penn State calls the opposite kind well-graded. Penn State describes well-graded aggregates as dense mixtures with few air voids between the stones, not suitable for drainage but preferred where compaction is important, such as pipe bedding, fill, and road surfaces. Wisconsin’s Department of Transportation defines a dense graded aggregate as a well-graded aggregate proportioned to contain a relatively small percentage of voids. Wisconsin’s glossary uses the words a little differently: it defines an open graded aggregate as a well graded aggregate containing little or no fine aggregate, with a relatively large percentage of voids.

Put together, the two descriptions are a trade: the stone that drains is not the stone that packs.

Crusher run and pea gravel: names the sources do not define

“Crusher run” is not an entry in the Wisconsin DOT glossary checked for this guide. One entry that mentions a crusher is “breaker run,” which that glossary defines as aggregate composed of very large particles from a primary crusher that has not been separated by screens into standardized sizes. That is Wisconsin’s definition of Wisconsin’s term. It should not be read as what a supplier in another state means by crusher run.

“Pea gravel” and “#411” do not appear in any of the three sources either, so this guide gives no size or behavior for them.

One thing the sources do say about natural, uncrushed gravel comes from Penn State, writing about Pennsylvania: bankrun gravel is typically rounded in shape and must be crushed before use.

Pennsylvania has its own names, so ask what is in it

In Pennsylvania even a numbered size has a local name. Penn State’s table lists AASHTO #57 under the Pennsylvania name 2B. It also says that “modified,” a term used by many municipalities and quarries, is not an official specification.

So when you call a supplier, the name is the start of the question. Ask:

• What is the largest stone in it, and what is the smallest?
• Does it contain fines, or is it washed clean?
• Is it crushed stone or rounded stone?
• What do you sell it for: drainage, a base, or a surface?
• How many tons are in a cubic yard of it?

The last answer goes into this site’s Gravel Calculator, which turns cubic yards into tons using 1.4 tons per cubic yard unless you enter your own figure. This guide gives no weight for any particular type of gravel. The supplier’s number is the one to use.

Choosing by use

What you need it to do	Kind of aggregate	Where that comes from
Let water through	Open-graded, clean stone such as #57	Penn State lists base material and subsurface drainage as uses for open-graded aggregates
Pack into a firm layer	Well-graded stone with fines	Penn State lists pipe bedding, fill, and road surfaces

These are uses on roads, in a Pennsylvania publication. For a driveway, a path, or a drain at your house, describe the job to the supplier and ask which of their products they would use for it.