Types of Gravel: Sizes, Uses, and a Visual Guide
An in-depth guide to gravel types, AASHTO size grades (#57, #8, #4, 3/4-inch, MOT Type 1), regional names (CA6, 21AA, ABC), and what each is best used for.
Walk into any quarry and you'll see a dozen piles of gray stone that all look the same. They're not. The difference between a #57 and a #8, or between pea gravel and decomposed granite, is the difference between a driveway that lasts twenty years and one that washes out in two. This guide breaks down what each common type and size actually is, what it's for, and how to spec it when you order.
Gravel vs. crushed stone — the actual definitions
In casual use, "gravel" means any small loose stone. In the trade, the distinction matters:
- Gravel is naturally weathered — usually pulled from riverbeds, quarries, or pits where water has rounded the edges. Pea gravel and river rock are true gravels. They're smooth and roll easily.
- Crushed stone is mechanically crushed bedrock. The fragments are angular with sharp faces that interlock and compact under load. Limestone, granite, and basalt are common parent rocks.
For any structural job — driveways, paver bases, French drains, retaining wall backfill — you almost always want crushed stone. For decorative beds, paths, and play areas, true gravel is fine.
Gravel size chart
The US uses a numbering system for crushed stone sizes (lower number = larger stone). The UK uses millimeter sizes and named specs like MOT Type 1.
| Size grade | Approx. size | Common name | Primary use |
|---|---|---|---|
| #1 | 2.5–4 inches | Large rip-rap | Erosion control, riverbanks |
| #2 | 1.5–2.5 inches | Coarse drainage | Heavy drainage, deep base |
| #3 | 1.5–2 inches | Coarse base | Sub-base for thick driveways |
| #4 | 1.5–2.5 inches | Drainage / base | French drains, base under #57 |
| #5 | 1 inch | Crushed stone | Driveways, parking lots |
| #57 | 3/4 inch | 57 stone | Driveways, drainage, French drains |
| #67 | 3/4 inch | 67 stone | Concrete aggregate, drainage |
| #8 | 3/8 inch | Pea-stone size | Paver bedding, fine surfaces |
| #10 | Stone dust | Screenings / fines | Paver joint filler, paths |
| 10mm (UK) | ≈ 3/8 inch | 10mm gravel | Resin-bound paths, decorative |
| 20mm (UK) | ≈ 3/4 inch | 20mm gravel | Driveways, paths |
| MOT Type 1 | 0–40mm graded | Type 1 sub-base | Sub-base under paving and driveways |
Gravel types in detail
Pea gravel
Smooth, rounded, 3/8-inch stones. Typically tan, gray, or mixed color. Comfortable underfoot, easy to rake, drains well. The downsides: it rolls, it migrates onto adjacent surfaces, and it doesn't compact. Best for paths, play areas, dog runs, and decorative ground cover. Don't use on slopes or anywhere vehicles drive.
Crushed stone #57
The workhorse. Angular fragments roughly 3/4 inch across, no fines. Drains well, compacts loosely (the angular faces lock against each other), and is stocked everywhere in the US. Use it as the top course on driveways, the surround for perforated drain pipe, the bedding for pavers, or as a clean drainage layer behind retaining walls.
Crushed stone #8
About half the size of #57 — 3/8 to 1/2 inch. Used as a leveling course on top of larger stone, as paver bedding (1 inch deep over a compacted base), or as a finer surface for foot-traffic areas.
Crushed stone #4
Larger — 1.5 to 2.5 inches. Use it as a deep drainage layer or as a thick sub-base under #57 in heavy-traffic driveways. Not walkable on its own; rocks are large enough to roll an ankle.
River rock
Smooth, rounded stones 1 to 3 inches across. Pretty in dry creek beds, decorative beds, and around pool patios. Doesn't compact at all — never use under pavers or on a driveway. Heavy and migrates downhill on slopes.
Decomposed granite (DG)
Crushed granite reduced to a sandy, fine texture. Compacts to a firm but permeable surface. Common for paths, bocce courts, and xeriscape mulch in the western US. Tan to gold in color. Tracks indoors more than coarser gravels.
Crushed limestone
A specific parent rock — calcium carbonate. Bright gray-white when fresh, weathering to a soft tan. Tighter compaction than granite or basalt at the same size. Most quarry-grade stone in the eastern US is limestone.
CA6 / 21AA / Class 5 (dense-grade base)
Same product, different regional names. A graded crushed stone (typically limestone or granite) with fines included — meaning the mix has stones from 1 inch all the way down to dust. The fines pack between the larger stones and the result compacts to near-concrete hardness. This is the right material under any paver patio, driveway, or shed pad.
ABC / Crusher run
The Southern US name for a similar dense-grade base aggregate. Functionally interchangeable with CA6 in most projects.
Recycled concrete
Crushed-up demolition concrete. Behaves mechanically like crushed limestone — angular, compacts well, drains well — and is usually 30–50% cheaper. The look is utilitarian (gray with bits of rebar dust visible) so it's usually used as a base layer or for full driveways where appearance doesn't matter.
Lava rock
Lightweight (~1,500 lb/yd³ vs. 2,700 for crushed stone), dark red or black, porous. Decorative mulch substitute, especially in arid landscapes. Won't compact, fades in UV over years.
Which gravel for which project
| Project | Recommended | Avoid |
|---|---|---|
| Driveway base | CA6 / ABC / 21AA / Class 5 | Pea gravel, river rock |
| Driveway top course | #57 limestone or granite | Pea gravel alone |
| Paver patio base | CA6 + 1" of #8 bedding | Topsoil, sand alone |
| French drain | #57 around perforated pipe | Anything with fines |
| Walking path | Pea gravel or DG over compacted base | Loose river rock |
| Decorative bed | River rock, lava rock, or pea gravel | — |
| Drainage behind retaining wall | #57 (angular, drains free) | Sand, dense-grade |
| Aquarium substrate | Pea gravel (washed), specialty substrates | Limestone (raises pH) |
| Concrete mix aggregate | #67 or #8 washed | Anything with clay fines |
Buying tips
- Specify washed or unwashed. Washed stone has the fines rinsed out, making it cleaner and better-draining but more expensive. Use washed for any visible top course and for drainage.
- Ask about minimum loads. Most quarries have a 1-ton or 1-yard minimum and a small-load surcharge below that. If you need less, buy bagged.
- Check the parent rock. "#57" can be limestone, granite, or trap rock depending on the quarry. They look and weather differently.
- Match size to use. Bigger is not better. A 1.5-inch driveway top course will hurt to walk on barefoot and will roll an ankle in the wrong shoe.
- Get a sample. Most quarries will let you take home a 5-gallon bucket so you can see the actual color and size before ordering 10 tons.