Gravel Sizes and Types: #57, #8, Crusher Run, and More

Ask a quarry for gravel and the first question back is usually “what size?” The answer is a number such as #57 or #8, or a name such as crusher run, and each one stands for a specific mix of stone sizes that a specification defines with sieves. This guide explains how the numbers work, shows one state's size chart, and sorts out the names that change from place to place, so you can match the product to the job before you work out how much to buy with the gravel calculator.

How gravel size numbers work

A size number is shorthand for a gradation: the share of the stone, by weight, that passes each sieve in a stack. Penn State's Center for Dirt and Gravel Road Studies describes the test as “filtering an aggregate through successively smaller sieves and measuring the weight retained on each sieve.” The national standard behind the numbers is ASTM D448, which “defines aggregate size number designations and standard size ranges” for highway and bridge work. State transportation departments then publish their own tables; Ohio's, for example, falls back on “the size specified in the material specification, the construction item, or as shown in AASHTO M 43.”

• A bigger number means smaller stone. In Penn State's summary, AASHTO numbers sizes from 1 to 10, “with 1 being the largest (all material passing a 4″ sieve opening) and 10 being the smallest (all material passing a 3/8″ sieve opening).”
• Two or three digits mean a blend. Penn State's example: “AASHTO 57 is a blend of AASHTO 5 and AASHTO 7.”
• Sieves come in two kinds. Inch sizes are square openings. Numbered sieves are “those of the U.S. Standard Sieve Series”; Ohio's specification lists the No. 4 at 4.75 mm and the No. 200 at 75 µm.
• The number says nothing about shape or rock. Virginia's coarse aggregate may be “crushed stone, crushed slag, crushed or uncrushed gravel, or lightweight aggregate” and still meet a size number.

Gravel size chart: Virginia DOT Table II-3

The Virginia DOT Road and Bridge Specifications (2020) list 15 open-graded sizes in Table II-3, “Sizes of Open-Graded Coarse Aggregates.” Each cell is the percent by weight finer than that sieve. “Min. 100” marks the sieve every stone passes, and “Max. 5” means no more than 5% may pass. VDOT uses these sizes for concrete, asphalt, surface treatments, and drainage.

Transcribed from VDOT's 2020 Road and Bridge Specifications, Section 203, Table II-3. This is one state's table: other states and suppliers can grade the same size number differently, so ask for the gradation of the product you buy.

#57 vs. #8 stone

No. 57 is the coarser of the two. Every piece passes a 1½ in sieve, 95–100% passes 1 in, and only 25–60% passes ½ in. No. 8 is finer: every piece passes ½ in, 85–100% passes 3/8 in, and 10–30% passes the No. 4 sieve. Both are clean. No. 57 lets at most 5% through the No. 8 sieve, and No. 8 at most 5% through No. 16.

In Pennsylvania the same two sizes go by other names. Penn State lists AASHTO #57 as PennDOT “2B” and #8 as “1B,” describing #8 as clean stone for “chip surfacing.”

Clean stone vs. dense-graded base

Every size in Table II-3 is open-graded, or clean. Penn State describes clean aggregates as “‘porous’ with notable air voids between individual stones, and little to no ‘fines’,” adding that they “drain effectively, but do not compact well to form a dense conglomerate.” A dense-graded (well-graded) mix is the opposite, with “few air voids between individual stones”: “not suitable for drainage but … preferred for use when compaction is important such as pipe bedding, fill, and road surfaces.”

Virginia grades its dense-graded subbase and base, the “material used to form a foundation for base or surface pavement,” to Table II-9. Compare the finest sieves: 21A keeps 6–12% passing the No. 200 sieve, while No. 57 allows no more than 5% through the much coarser No. 8.

A design range: each producer's job-mix formula falls within it, and VDOT's Table II-10 tolerances apply. Numbered sieves are those of the U.S. Standard Sieve Series.

Crusher run, #411, and other regional names

Most of the confusion comes from names that are not size numbers. Their meaning depends on the state, so each one below is tied to the specification that defines it.

Crusher run (Virginia)

Virginia defines crusher run as aggregate crushed from stone, slag, or gravel that “shall contain all of the sizes produced when the original aggregate is reduced through a series of crushers to the maximum size specified.” Its stated uses are “backfilling and bedding pipe and box culverts, maintaining traffic, and repairing and constructing all-weather private access pavements.” Size 25 has 32±18% passing the No. 4 sieve, where No. 57 allows at most 10%.

Cells as printed in VDOT's Section 205.03(a); 95±5 means 90 to 100 percent.

#411 (Ohio)

There is no size 411 in Virginia's table. Ohio DOT's specifications have an Item 411, Stabilized Crushed Aggregate: “placing a compacted course or courses of crushed aggregate,” in compacted lifts of no more than 6 in. Its gradation runs from 100% passing 1 1/2 inch (37.5 mm) through 30 to 60% passing No. 4 (4.75 mm) to 3 to 15% passing No. 200 (75 µm), so it carries fines like a dense-graded base. A product sold as “#411” elsewhere may or may not be made to Ohio's gradation, so ask the supplier which specification it meets.

2A, 2B, and “modified” (Pennsylvania)

Penn State describes PennDOT 2A as a base for placing asphalt with a 2 in top size and fines that are “allowed to vary from 0-10%.” It also warns that “‘modified’ is NOT an official specification,” even though many municipalities and quarries use the term.

Pea gravel and rounded stone

Pea gravel has no size number in Virginia's table or in Penn State's list of common Pennsylvania aggregates, so its size is whatever the supplier screens it to. Ask for the sieve it passes and its gradation, the same as for any other product.

Shape matters as much as size. Penn State says bankrun gravel is “typically rounded in shape and must be crushed before use” as a road aggregate. The driveway layers guide covers why driveway surfaces use crushed stone with fines instead.

Where loose fill is the point, pea gravel has a documented use. The CPSC's home playground handbook lists sand or pea gravel as protective surfacing for equipment up to 5 ft high, at least 9 in deep. For equipment up to 8 ft it lists wood mulch or chips, engineered wood fiber, or shredded rubber mulch instead.

Which size for which job

ASTM notes that some contract documents “specify certain aggregate sizes for specific uses.” These are the uses the sources here name. For your own project, follow your plans, local code, and the supplier's advice for your soil and climate.

Uses as written in each source, for public works (VDOT, PennDOT) and home playgrounds (CPSC). They are examples, not a design.

For a patio, the base and bedding materials and their depths come from the paver manufacturer's installation guide. Enter those depths in the paver calculator to get the volume of each layer along with the paver count.

How size and type change your order

• Volume does not depend on size. Length × width × depth gives the same number of cubic yards whether you fill it with No. 57 or No. 8. The gravel calculator works this way for every product.
• Weight depends on the product. When Ohio DOT has to convert Item 411 from weight to compacted volume, it counts 3,800 lb of crushed stone or 3,900 lb of crushed gravel as one cubic yard. Your supplier's figure for the exact product is the one to use; see how much a yard of gravel weighs.
• Compacted volume is smaller than loose. Ohio pays for Item 411 by the cubic yard “compacted in place.” Compaction shrinks a loose load, so order more loose material than the finished volume.
• Loose fill settles. CPSC notes that an initial 12 in of playground surfacing compresses to about 9 in over time, which the worked example below builds in.

Worked example: pea gravel under a play set

A backyard climber with a 10 × 8 ft frame, platforms no higher than 5 ft, and no swings. CPSC calls for surfacing at least 6 ft beyond the equipment in all directions and, for pea gravel, an initial fill of 12 in that compresses to about 9 in.

Surfaced area = (10 + 2 × 6) × (8 + 2 × 6) = 22 × 20 ft = 440 sq ft
Volume        = 440 sq ft × (12 ÷ 12) ft = 440 ft³ = 16.3 yd³
Order         = round up to ½ yd³ steps = 16.5 yd³

The 12 in depth already allows for compression, so no extra allowance is added here; add one if the ground is uneven. CPSC also says the surfacing “should be periodically refilled to maintain at least a 9-inch depth,” so expect to top it up. A swing needs more room: the handbook extends surfacing in front of and behind it to twice the height of the top bar. Run your own area in the gravel calculator, and if you buy by the ton, enter your supplier's density for that pea gravel.