Stone calculator
2A Modified Stone Calculator
2A modified is the Pennsylvania spec base stone — crushed rock with fines that compacts to a hard, sealed sub-base. Enter area and compacted depth.
Your project
Driveways 4-6" compacted. Under a shed or slab, 4". Under heavy truck traffic, 8".
Crews typically order 5-10% extra to cover compaction, spillage and uneven subgrade.
Delivered 2a modified stone typically runs $22-$45 per ton.
2A modified stone needed
11.34
US tons · includes 5% waste
- Area
- 480 sq ft
- Volume
- 6.22 cubic yards
- Volume (cubic feet)
- 168 cu ft
- Total weight
- 22,680 lb
- Density used
- 135 lb per cu ft (1.82 tons/yd³)
- Truckloads (15-ton)
- 1
- Estimated delivered cost
- $386
Quarry densities vary by source and moisture. Confirm tons per cubic yard with your supplier before placing a bulk order — a 10% density difference is a whole extra load on a big job.
The shareable link reopens this calculator with your exact inputs.
What 2a modified stone is
PennDOT 2A modified is crushed limestone or gravel graded from 1.5 inch down to dust. The fines are what make it "modified" — they fill every void so the material compacts to roughly 135 lb per cubic foot, close to 1.8 tons per cubic yard, far denser than clean stone.
At 135 lb per cubic foot, one cubic yard weighs about 1.82 US tons, and one ton spread 2" deep covers roughly 89 square feet.
How to install it
Place in 4 inch maximum lifts and compact each one with a plate or roller, lightly wetted. Compacted 2A will not rut under a loaded truck; the same material dumped and left loose will.
The mistake that costs the most
Using it where water has to drain through. 2A sheds water by design. Behind a retaining wall or in a French drain it functions as a dam, and the wall or drain fails. Clean #57 goes in drainage zones; 2A goes under things.
The math behind the calculator
Square feet × (depth in inches ÷ 12) = cubic feet. Cubic feet ÷ 27 = cubic yards. Cubic feet × 135 ÷ 2,000 = US tons. The waste allowance is applied to the volume before the weight conversion, which is how suppliers quote it.
2A modified stone needed per 100 square feet
At 135 lb per cubic foot, before waste.
| Depth | Cubic feet | Cubic yards | Tons |
|---|---|---|---|
| 1" | 8.3 | 0.31 | 0.56 |
| 2" | 16.7 | 0.62 | 1.12 |
| 3" | 25 | 0.93 | 1.69 |
| 4" | 33.3 | 1.23 | 2.25 |
| 6" | 50 | 1.85 | 3.38 |
| 12" | 100 | 3.7 | 6.75 |
Recommended depth by application
| Application | Depth |
|---|---|
| Shed / slab sub-base | 4" compacted |
| Residential driveway base | 4-6" compacted |
| Paver patio base | 4" compacted |
| Commercial / truck traffic | 8-12" compacted |
Frequently asked questions
+How many tons of 2a modified stone do I need?
Multiply square feet by depth in feet to get cubic feet, then multiply by 135 and divide by 2,000. A 500 sq ft area at 4" needs about 11.25 tons before waste.
+How many tons of 2a modified stone are in a cubic yard?
Roughly 1.82 tons at 135 lb per cubic foot. Wet material weighs 5-10% more, which matters when you are buying by the ton and measuring by the yard.
+How deep should 2a modified stone be?
Shed / slab sub-base: 4" compacted. Residential driveway base: 4-6" compacted. Paver patio base: 4" compacted. Commercial / truck traffic: 8-12" compacted.
+What does 2a modified stone cost?
$22 – $45 per ton delivered in most US markets, before the haul fee. Short loads carry a minimum charge, so half a load often costs nearly as much as a full one.
+How many tons of 2A modified in a cubic yard?
About 1.8 tons compacted, using 135 lb per cubic foot. Loose out of the truck it runs closer to 1.5 tons per cubic yard, which is why suppliers quote tons and not yards.