2A & 2B Stone Calculator (PennDOT)
Pennsylvania quarries sell stone by PennDOT name: 2A is a well-graded base stone from 2 in down to fines, 2B is clean stone equal to AASHTO #57, 1B is #8, 3A is #3 and #4 is AASHTO #1 ballast. Pick the stone, enter the area and depth, and the calculator returns cubic yards, tons, truck loads and a cost range — adding the compaction allowance for 2A, which shrinks as its fines pack into the gaps.
PennDOT stone names and what they mean
| PA name | AASHTO | Size | Tons / yd³ | Used for |
|---|---|---|---|---|
| PennDOT #4 (ballast) | AASHTO #1 | 4" – 3/4" clean | 1.35 | Construction entrances, underdrains, bottom course over soft ground |
| PennDOT 2A (2A modified) | — (well graded) | 2" down to fines | 1.5 | Base and sub-base under asphalt, pavers and sheds; pipe bedding; compacted driveway base |
| PennDOT 2B | AASHTO #57 | 1.5" – 3/32" clean | 1.4 | Drainage: French drains, footing drains, under-slab stone, driveway top layer |
| PennDOT 1B | AASHTO #8 | 1/2" – 3/32" clean | 1.4 | Chip surfacing, paver setting bed, walkable topping |
| PennDOT 3A | AASHTO #3 | 2.5" – 1/2" clean | 1.35 | Coarse drainage layer and driveway bottom course |
Names and sizes are from Penn State's Center for Dirt and Gravel Road Studies bulletin Aggregates 101. 2A is "well graded" — it carries every size from 2 in down to dust (24–50% passes a #4 sieve and up to 10% passes #200) — so it packs into a hard layer. 2B, 1B, 3A and #4 are "open graded": clean stone with the fines washed out, so water runs straight through.
Worked example: a 60 × 12 ft driveway
| Layer | Depth | Tons | Tri-axle loads |
|---|---|---|---|
| PennDOT 2A (2A modified) | 6 in | 27.3 | 2 |
| PennDOT 2B | 3 in | 9.8 | 1 |
6 in of compacted 2A for the base and 3 in of 2B on top is a common Pennsylvania build. 2A gets a 30% allowance because its fines pack into the gaps (the same figure as the crusher run calculator); clean 2B barely compacts.
Which one do I need?
- Base under a driveway, shed or patio: 2A (or "2A modified" — a quarry's 2A with extra fines; not an official spec).
- French drain, footing drain, under a slab: 2B, wrapped in fabric — see the French drain calculator.
- Driveway top layer: 2B, or 1B for a smoother surface.
- Soft ground or a construction entrance: #4 ballast, then 2A over it.
Outside Pennsylvania, order by AASHTO number: the #57 stone calculator is the same stone as 2B. For the whole layered driveway, use the gravel driveway calculator, and to see how many trucks it takes, the dump truck load calculator.
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Frequently asked questions
- What is 2B stone?
- PennDOT 2B is clean crushed stone from about 1.5 in down to 3/32 in, with almost no fines — the Pennsylvania name for AASHTO #57 stone. It drains freely, so it's used for French drains, footing drains, under slabs and as a driveway top layer.
- What is 2A stone?
- PennDOT 2A is a well-graded stone from 2 in down to fines (up to 10% passing the #200 sieve). It was designed as a base under asphalt and compacts into a firm layer, so it's the usual base for driveways, patios, sheds and pipe bedding. "2A modified" isn't an official spec — it usually means 2A with extra fines added to bind it.
- How many tons of 2A do I need for a driveway?
- For a 60 × 12 ft driveway base 6 in deep: 13.3 yd³ in place, plus 30% because 2A compacts and 5% extra, is 18.2 yd³ — about 27.3 tons, or two tri-axle loads.
- How much does a yard of 2B stone weigh?
- About 1.4 tons (2,800 lb) per cubic yard, the same as #57 stone. 2A is heavier per yard, about 1.5 tons, because its fines fill the gaps between the stones.
- Is 2B the same as #57 stone?
- Yes. Penn State's Center for Dirt and Gravel Road Studies lists PennDOT 2B as AASHTO #57, 1B as #8, 3A as #3 and #4 as AASHTO #1. Outside Pennsylvania, ask for the AASHTO number.
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