21A Gravel: Virginia Base Stone (and 21AA in Michigan)

21A gravel is a dense-graded crushed stone base named for a Virginia Department of Transportation aggregate gradation. It mixes stones of many sizes, up to roughly an inch to an inch and a half, with enough fines to compact into a hard, stable layer. Contractors in Virginia and nearby areas use 21A under driveways, sidewalks, slabs, and parking areas. A similar name, 21AA, refers to a Michigan DOT dense-graded aggregate used the same way.

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21A vs 21B

Product	Fines content	Behavior	Typical use
21A	More fines	Packs very tightly, smoother surface	Base under pavement, slabs, driveway surfaces
21B	Fewer fines	Drains a bit better, slightly coarser	Base course, subbase, areas needing drainage

Both are dense-graded and compact well. Suppliers may carry one or both, and exact gradations follow VDOT specifications and the quarry’s product.

Michigan 21AA

Michigan’s 21AA is a dense-graded aggregate, often about 1-inch minus, made from crushed limestone, natural gravel, or crushed concrete. Homeowners use it for driveway bases and gravel driveways. It behaves much like Virginia 21A, but it is a separate state specification.

Weight and coverage

Dense-graded aggregates like 21A typically weigh around 1.4 to 1.5 tons per compacted cubic yard.

Driveway area	4 inches	6 inches
10 x 40 feet	About 7 tons	About 10.4 to 11 tons
12 x 60 feet	About 12.5 to 13.3 tons	About 18.7 to 20 tons
20 x 40 feet	About 13.9 to 14.8 tons	About 20.8 to 22.2 tons

Add 10 to 15 percent for compaction and waste. Use the base calculator for your dimensions.

Uses

Driveway base and surface. 21A makes a firm, smooth gravel driveway, though it can get dusty.
Base under asphalt paving.
Base under concrete slabs and sidewalks.
Paver base beneath a bedding layer.
Shed and building pads.

Installing 21A

Excavate to firm subgrade and remove organic material.
Use a geotextile on soft or clay soil.
Place 21A in lifts of about 3 to 4 inches.
Moisten and compact with a plate compactor or roller.
Shape a crown or cross slope for drainage.

Too dry, and it will not compact well; too wet, and it can pump or rut. See dense-grade aggregate driveways for more.

Bottom line

21A gravel is a Virginia dense-graded base stone with fines that compacts into a hard layer for driveways, slabs, and pavement. 21B is slightly coarser with fewer fines, and Michigan’s 21AA is a similar product under a different state spec. Plan on about 1.4 to 1.5 tons per compacted yard, plus extra.

Questions people ask

What is 21A gravel?

A dense-graded crushed stone base with fines, named under a Virginia DOT gradation, used under driveways and slabs.

What is the difference between 21A and 21B?

21A has more fines and packs tighter; 21B has fewer fines and is slightly coarser.

Is 21AA the same as 21A?

They are similar dense-graded bases but come from different state specs: 21AA is Michigan, 21A is Virginia.

How much does 21A gravel weigh?

Around 1.4 to 1.5 tons per compacted cubic yard.

Is 21A good for a driveway?

Yes. It compacts into a firm surface and makes an excellent driveway base.

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