Gravel isn’t one material — it’s a dozen quarried products sold under a numbering system that confuses everyone once, and a weight-per-yard that swings by a factor of two between types. Both matter for ordering: pick the wrong type and it won’t compact or drain the way you need; use the wrong weight and your ton order lands wrong. Here’s the field guide.

The # number system

The numbers refer to sieve grades — smaller number, bigger stone. You don’t need the spec to buy gravel; you need what each size is for:

Type	Typical size	Weight/yd³	Best for
#3 / #4 crushed stone	1½–2½ in	~2,600–2,800 lb	Drainage, driveway base, backfill
#57 crushed stone	½–1¼ in	~2,700 lb	Driveways, drains, concrete aggregate — the default
#8 / #67 crushed stone	⅜–¾ in	~2,600 lb	Surface dressing, paths, mixing
Pea gravel	~⅜ in round	~2,450 lb	Walkways, dog runs, around plants
River rock	1–3 in round	~2,600 lb	Beds, edging, dry creek beds
Crusher run / road base	dust–1½ in mixed	~3,000 lb	Driveway bases, paver base — compacts hard
Decomposed granite	≤⅜ in + fines	~2,550 lb	Paths, xeriscaping, bocce courts
Lava rock	¾–1½ in	~1,500 lb	Mulch substitute, fire pits — lightest
Riprap	6–12+ in	~2,800–3,000 lb	Erosion control, slopes, shorelines

Two caveats. Sizes vary by quarry — “#57” is a common spec name, not a universal exact dimension. And the weights are typical industry figures from published supplier tables (sources) — real loads vary with moisture and source rock, which is why the gravel calculator keeps density as an editable field instead of a hidden constant.

Choosing by job

Driveways and parking: you want angular, locking material — crusher run for the base, #57 for the surface (or crusher run alone for a single-product drive). Round stone like pea gravel migrates under tires and won’t hold a crown.

Drainage and French drains: #57 or #8 — open-graded crushed stone with voids for water, no fines that clog. Pea gravel drains too but the round shape is easier to shift during installation.

Walkways and play: pea gravel or DG — comfortable underfoot, inexpensive. DG compacts into a firmer surface; pea gravel stays loose and casual.

Mulch substitute around plants: pea gravel, river rock or lava rock — stone doesn’t decompose, so a 1–2 in layer is permanent and keeps weeds down. Lava rock’s low density is why it’s sold by the bag as often as by the yard.

Under a concrete slab or pavers: crushed stone or crusher run, compacted — never pea gravel, which shifts. The paver calculator assumes the standard compacted-base spec; the concrete calculator assumes a compacted base under slabs that aren’t on engineered fill.

A word on tons vs yards

Suppliers sell gravel by the cubic yard (volume) or the ton (weight), and a yard is not a fixed weight — it’s ~1,500 lb of lava rock or ~3,000 lb of crusher run. “How many tons in a yard” has a different answer for every row of that table. If your supplier quotes tons, convert with their material’s real density — or run the numbers in the gravel calculator, which does the conversion from your volume to the tonnage with your material preset (or a custom density if the scale house disagrees).

Frequently asked questions

What is #57 gravel and what is it used for?

#57 is crushed stone roughly ½–1¼ in — angular pieces that lock together and drain well. It's the default for driveways, drainage, French drains and concrete aggregate: about 2,700 lb/yd³ typically. The '#' number comes from a grading sieve spec — bigger number, smaller stone.

What's the difference between pea gravel and crushed stone?

Pea gravel is small (⅜ in) round stone — comfortable underfoot, good-looking, but the round shape doesn't compact or lock, so it migrates and doesn't hold a slope. Crushed stone is angular — it compacts and stays put, which is why it's the driveway/drainage default. Same volume, different job.

What is crusher run gravel?

Crusher run (road base, crushed aggregate base, 'dense grade') is crushed stone including the dust and fines — roughly 0–1½ in all mixed together. The fines fill the gaps when compacted, so it locks hard and sheds water — the standard base under driveways, roads and pavers. Heavy: ~3,000 lb/yd³.

How much does a cubic yard of gravel weigh by type?

Typical ranges: lava rock ~1,500 lb, pea gravel ~2,450, decomposed granite ~2,550, river rock ~2,600, #57 crushed stone ~2,700, crusher run ~3,000 lb/yd³. These are industry-typical figures, not specs — moisture and quarry source move them. The gravel calculator uses these same presets and lets you edit the density.

What size gravel should I use for a driveway?

The usual layered answer: a coarser, locking base (crusher run or #3/#4 stone, 4+ in compacted), then a finish layer of #57 or pea-sized stone for the surface. One material for the whole driveway is a compromise — crusher run alone is the common single-material pick because it both compacts and looks presentable.

What is decomposed granite good for?

DG is weathered granite ground to ⅜ in minus — it compacts into a firm, natural-looking surface for paths, patios and bocce courts, and it's the standard xeriscape mulch in dry climates. ~2,550 lb/yd³. Stabilizer (a binder) helps it hold together on slopes; unstabilized, it shifts under traffic.