PA Gravel Names and Sizes: 2A, 2B, #57, 2RC and What Each Is For

Pennsylvania quarries sell stone by PennDOT and AASHTO size numbers: 2A is PennDOT’s dense-graded base that packs hard, 2B is the yard name for AASHTO No. 57 clean stone that drains, and 1B is No. 8 half-inch chip. The gradations below come from PennDOT’s Publication 408 specifications, and the yard names from Penn State’s Center for Dirt and Gravel Road Studies. After that is the stone we’d use for patios, driveways, walls and drains.

What do Pennsylvania gravel names mean?

PennDOT’s aggregate table (Section 703.2, Table C) lists clean stone by its AASHTO number and adds two PennDOT-only sizes, 2A and OGS. Quarries and contractors still use Pennsylvania yard names for several of the AASHTO sizes. Penn State’s Center for Dirt and Gravel Road Studies lists these matches in its Aggregate 101 guide:

Yard name	Spec number	Size	Type
2A	PennDOT No. 2A	2 in. to dust	Dense-graded base
2A modified	Not a spec name; usually 2A with fines added	2 in. to dust	Dense-graded base
2B	AASHTO No. 57	1½ in. to about 3/32 in.	Clean, drains
1B	AASHTO No. 8	½ in. to about 3/32 in.	Clean chip
3A	AASHTO No. 3	2½ in. to ½ in.	Clean
#4s, ballast	AASHTO No. 1	4 in. to ¾ in.	Clean
Grit, screenings	AASHTO No. 10	3/8 in. and finer	Fine
2RC	PennDOT select granular material	2 in. down, varies widely	Well-graded fill
R-3	PennDOT rock lining R-3	About 2 to 6 in.	Rock lining
R-4	PennDOT rock lining R-4	About 3 to 12 in.	Rock lining

How the AASHTO numbers work: Penn State explains that the base sizes run from 1 to 10 by the largest stone, with No. 1 passing a 4-inch sieve and No. 10 passing a 3/8-inch sieve. Two-digit sizes blend two base sizes, so No. 57 is a blend of No. 5 and No. 7. PennDOT’s table also lists No. 67, a clean stone from 1 inch down.

What is 2A stone?

2A is PennDOT’s own size, not an AASHTO number. It runs from 2 inches down to dust, so the small stone and fines fill the gaps between the big stones and the layer locks up when it’s compacted. PennDOT uses it as subbase under pavement (Section 350) and as trench backfill along the sides of pipe, and over the pipe in some cases under roadways (Section 601). These are its limits in the 2020 specification:

Sieve	Percent passing (No. 2A)
2 in.	100
¾ in.	52 to 100
3/8 in.	36 to 70
No. 4	24 to 50
No. 16	10 to 30
No. 200 (fines)	0 to 10 when used as subbase (Table D)

How PennDOT builds a 2A subbase (Section 350):

• Stone of Type S quality or better, No. 2A and/or No. OGS.
• Compacted layers no thicker than 8 inches, and at least 3 inches for 2A (4 inches for OGS).
• Compacted until the stone no longer moves under the roller, working from the sides toward the center.

PennDOT allows crushed concrete from public pavement and structure projects to be used as 2A, but not in subbase, so ask before you assume a recycled 2A meets the spec.

What is 2A modified?

Penn State says “modified” isn’t an official specification. It usually means 2A with fines added so it grades out more evenly and packs tighter. Because 2A itself can carry anywhere from 0 to 10 percent fines, Penn State notes one load can behave more like open stone and another more like a dense base. If the job depends on it, ask the quarry whether its 2A is PennDOT-certified and what its “modified” actually is.

How big is 2B (No. 57) and the other clean stone?

Clean stone has almost no fines, so water runs through the gaps. It doesn’t compact into a tight layer the way 2A does. These are PennDOT’s Table C limits for the clean sizes you’ll be offered in Pennsylvania:

Size (yard name)	Percent passing each sieve
No. 1 (#4s)	4 in.: 100 · 3½ in.: 90–100 · 2½ in.: 25–60 · 1½ in.: 0–15 · ¾ in.: 0–5
No. 3 (3A)	2½ in.: 100 · 2 in.: 90–100 · 1½ in.: 35–70 · 1 in.: 0–15 · ½ in.: 0–5
No. 57 (2B)	1½ in.: 100 · 1 in.: 95–100 · ½ in.: 25–60 · No. 4: 0–10 · No. 8: 0–5
No. 67	1 in.: 100 · ¾ in.: 90–100 · 3/8 in.: 20–55 · No. 4: 0–10 · No. 8: 0–5
No. 8 (1B)	½ in.: 100 · 3/8 in.: 85–100 · No. 4: 10–30 · No. 8: 0–10 · No. 16: 0–5
No. 10 (screenings)	3/8 in.: 100 · No. 4: 85–100 · No. 100: 10–30

Read No. 57 this way: almost all of it passes a 1-inch screen, a quarter to well over half passes ½ inch, and next to none is smaller than a No. 8 sieve (about 3/32 inch). That missing small stuff is why it drains.

What is 2RC, and is it the same as screenings?

No. 2RC is PennDOT’s select granular material (Section 703.3): 100 percent passes a 2-inch sieve, 15 to 60 percent passes a No. 4 sieve, up to 30 percent passes a No. 100 sieve, and no more than 10 percent can be deleterious shale. The bands are wide, and Penn State calls it “misc.” or “reclaim” material that varies widely, used for fill, pipe bedding and road surfaces.

Screenings are No. 10, everything 3/8 inch and finer. Neither one belongs under pavers. The Concrete Masonry and Hardscapes Association (CMHA) says paver bedding sand should meet ASTM C33 at a nominal 1 inch, uncompacted, and that limestone screenings, stone dust and masonry (mortar) sand shouldn’t be used for bedding. PennDOT’s own sands are Type A, its concrete sand (fineness modulus 2.30 to 3.15), and Type C, its mortar sand (1.6 to 2.5).

Which stone goes under a patio, driveway, wall or drain?

The rule that falls out of the specs: dense-graded 2A where you need strength and a flat, hard layer, clean stone where water has to move, and sand only as a thin bedding layer.

Job	Stone	What the source says
Paver patio or walk base	2A, compacted in layers	CMHA: at least 4 in. compacted over well-drained soil; thicker on continually wet or weak soil in colder climates
Paver bedding	Concrete sand (ASTM C33)	CMHA: nominal 1 in., uncompacted; no screenings or stone dust
Paver driveway base	2A	CMHA: at least 6 in. on well-drained soil
French drain or pipe underdrain	2B (No. 57)	PennDOT 610 (Type I backfill) and 612; CMHA: at least 3 in. of No. 57 around a drain pipe
Underdrain, PennDOT Type II backfill	1B (No. 8); PennDOT also lists Type A sand for Type II	PennDOT 610, Type II backfill
Block retaining wall	2B (No. 57) in the block cores and behind the wall	Another state’s spec as an example, North Carolina DOT’s segmental wall spec (Section 454): No. 57 in the cores and at least 12 in. behind the blocks, with fabric between stone and soil. PennDOT is not the source here.
Pipe or utility trench	2A along the sides of the pipe	PennDOT 601: 2A in compacted 4-in. layers along the sides; 2A over the pipe in some cases under roadways
Spring, sump or wet hole	No. 1 (#4s)	PennDOT 613: No. 1, or approved local stone topped with a 6-in. layer of No. 57
Ditch, swale or pipe outlet	R-3 or R-4	PennDOT 850: R-3 placed 12 in. thick, R-4 18 in. thick

Base depth is a minimum, not a target. CMHA’s numbers are for well-drained soil, and it says continually wet or weak soils in colder climates need thicker bases. On wet, clayey or frost-prone ground, plan more base and a way for water to get out of it. Check your own lot’s soil on USDA’s Web Soil Survey.

What size is R-3 and R-4 rock?

PennDOT’s rock lining spec (Section 850) grades rock by the percent passing square openings, using the National Crushed Stone Association size numbers:

Class	100% passes	15–50% passes	0–15% passes	Placed thickness
R-3	6 in.	3 in.	2 in.	12 in.
R-4	12 in.	6 in.	3 in.	18 in.

The rock has to be hard and angular with no shale seams, with a specific gravity of at least 2.5. It must come from a source of approved Type A aggregate or pass a petrographic exam. PennDOT has the full course placed in one operation, not in layers or by chute dumping. Larger classes run up to R-8.

Which edition of PennDOT’s spec is this?

The numbers above are from Publication 408/2020. PennDOT’s version index shows a 2026 edition in effect from April 10, 2026. We couldn’t open the 2026 file to compare, so check with your quarry before relying on an exact 2A limit. The AASHTO clean-stone sizes are national standard sizes that PennDOT lists by number, so they’re less likely to change between editions. Ask the quarry whether a load is PennDOT-certified if your job or your township requires it.

Sources

• PennDOT Publication 408/2020 (PDF): Sections 350, 601, 604, 610, 612, 613, 703 and 850
• PennDOT Publication 408 editions and effective dates (PDF)
• Penn State Center for Dirt and Gravel Road Studies, Aggregate 101
• CMHA, Construction of Interlocking Concrete Pavements (PAV-TEC-002)
• North Carolina DOT (NCDOT), Segmental Gravity Walls, Section 454 (PDF): a North Carolina spec, cited only as an example

Last checked November 14, 2026.

Common questions

Is 2B stone the same as #57?

Yes. Penn State’s Center for Dirt and Gravel Road Studies lists 2B as the Pennsylvania yard name for AASHTO No. 57, a clean stone from about 1 1/2 inches down to roughly 3/32 inch. In PennDOT’s spec, 95 to 100 percent passes a 1-inch sieve and no more than 5 percent passes a No. 8 sieve.

What is the difference between 2A and 2A modified?

2A is PennDOT’s dense-graded base, 2 inches down to dust, with up to 10 percent fines when used as subbase. Modified is not a PennDOT spec name. Penn State says it usually means 2A with fines added so it packs tighter, so ask the quarry what its modified actually is.

What gravel goes under pavers in Pennsylvania?

Compacted 2A for the base and about 1 inch of ASTM C33 concrete sand for bedding. The Concrete Masonry and Hardscapes Association calls for at least 4 inches of compacted base under patios and 6 inches under residential driveways on well-drained soil, more on wet or weak ground, and says not to use screenings or stone dust as bedding.

What is 2RC gravel?

2RC is PennDOT’s select granular material: all of it passes a 2-inch sieve, 15 to 60 percent passes a No. 4 sieve and up to 30 percent passes a No. 100 sieve. Penn State notes it varies widely and is used for fill and pipe bedding. It is not a paver base.

What size is R-4 rock?

In PennDOT’s rock lining spec, all R-4 passes a 12-inch opening, 15 to 50 percent passes 6 inches and up to 15 percent passes 3 inches, and it is placed 18 inches thick. R-3 is smaller, mostly 2 to 6 inches, and is placed 12 inches thick.

See every Pennsylvania building, digging and contractor rule on our Pennsylvania guide. Find stone near you with Pennsylvania quarries by county, and figure tons with our gravel calculator.