Types of Gravel, Sorted by the Work They Do

Stone that locks

Broken stone locks because every piece has flat faces and sharp corners. Press a load of it down and the pieces jam together, so a tire can cross without pushing them aside.

Four names cover this group: #67 Stone, #57 Crushed Stone, Driveway Gravel and 3/4" Crushed Stone. All four are crushed from solid rock, and they make the surface course on most working drives. Driveway Gravel, at 3/4 inch clean crushed, is the plain pick for that job.^[1]

Its weak spot is comfort. Nobody wants to cross it barefoot, and a kick stand or a chair leg will find the gaps. Clean crushed stone also needs something firm below it, or it slowly works its way into soft soil.

Stone that rolls

Round stone has no corners left to catch, so it moves. Water shaped both Pea Gravel, a 3/8 inch stone, and the larger River Rock, which starts at 1 inch and reaches 3. Both shift under a foot or a wheel the way marbles would.^[1]

For some jobs that is the whole appeal. Pea Gravel feels soft to walk on and gives a dog an easy surface. It settles level on its own and stays comfortable in bare feet.

Put a car on it and you will carve ruts by the weekend. Any slope makes things worse, since the stone creeps downhill a little with every step, and it needs a firm edge along the sides or it wanders into the lawn.

Stone that drains

Water moves through the empty space between stones, so a draining stone needs big gaps and no dust to clog them. That rules out anything labeled minus.

Drain Rock tops out at 1-1/2 inches and is the one made for this work, in French drains, soakaways and behind foundations. #4 Crushed Stone and Railroad Ballast go larger at 1-1/2 to 2-1/2 inches, with even wider gaps. #57 Crushed Stone serves too, with smaller gaps that still pass water freely.^[1]

In the ground, surrounding soil will try to fill those gaps over the years, so most drains wrap the stone in non-woven fabric.

Open stone does a poor job of carrying weight on its own. A wide layer of it under a car shifts and spreads unless something holds the edges in.

Stone that packs

Dense mixes keep their fines, and the fines change everything. Small particles sit in the spaces around larger ones, and when you dampen the layer and pass a plate compactor across it, the whole thing sets into a hard, close crust.

Road Base is the main one, at 3/4 inch minus. Crushed Concrete behaves in much the same way at the same size, and Asphalt Millings at 1 inch minus bind as sun and traffic work on them. Stone Dust Screenings and Decomposed Granite pack too, on a finer scale, for paths and paver beds.^[1]

This is the group that holds a driveway up. Lay it in thin lifts, compacting as you go, since a thick layer dumped all at once stays soft in the middle.

Those same fines slow any water that needs to go down. A packed layer sheds rain to the sides, so give it a crown or a slight fall, and keep it away from anywhere a drain needs to work.

Stone that decorates

Here color and shape do the job. River Rock brings mixed earth tones and round forms to a dry creek or a foundation band. Pea Gravel adds mixed tan and brown. Decomposed Granite lays down gold to tan, with a soft, close surface that looks at home on a garden path.^[1]

Walkway Gravel sits between looks and use, in mixed color at 3/8 inch.^[1]

You pay for looks. River Rock costs $841 for a 2 ton load at the median, and Pea Gravel costs $702. The same load of Driveway Gravel is $435.^[2]

So keep decorative stone in the places people see. Put plainer stone under it and behind it, where nobody looks.

Judge color with care, because wet stone looks darker than dry stone. A pile that seemed rich in the rain can look pale on a hot afternoon.

Riprap, the outlier

One stone in our catalog fits none of these groups. Riprap measures 6 to 12 inches, and its only job is to stay put while water tries to move it. Banks and outfalls are where you meet it, and on a wall or a bank that matters, follow the engineer's plan.^[1]

One lot, five jobs

Say one rural lot needs work in all five groups. The sums show how differently the jobs add up.

The lane is 64 feet by 9 feet, and it starts with packing stone. Four inches of Road Base is 192 cubic feet, or 7.11 yards, and at 2,800 lb to the yard that comes to 9.96 tons. Order 10 tons, which is $763 at the median.^[1],[2],[3]

Locking stone goes on top. Driveway Gravel at 2 inches is 96 cubic feet, or 3.56 yards, and 1.35 tons a yard makes 4.8 tons. That rounds up to 5 tons, at $616.^{[1],[2],[3],[4]}

A dog run of 16 feet by 15 feet wants rolling stone. Pea Gravel at 2 inches comes to 40 cubic feet, 1.48 yards and about 1.9 tons, so the 2 ton minimum covers it at $702.^{[1],[2],[3],[4]}

A soggy corner needs a trench 26 feet long, 1 foot wide and 1.5 feet deep. That is 39 cubic feet of Drain Rock, or 1.44 yards, which makes about 1.95 tons and fits a 2 ton order at $428.^[1],[2],[3]

Last, a decorative band of River Rock along the house, 30 feet by 3 feet at 3 inches, needs only 22.5 cubic feet, about 1.1 tons. The minimum applies again, and 2 tons costs $841. You will have plenty left to carry the band around a corner.^{[1],[2],[3],[4]}

When a job sits between two groups

A handful of stone tells you most of what you need. Sharp edges mean it will lock, and smooth sides mean it will roll. Dust left on your palm means it will pack. Clean hands and wide gaps mean it will drain.

Plenty of jobs ask for two things at once. Ask which one fails first.

A steep path needs grip more than softness, so locking or packing stone beats anything round. A patio that floods needs drainage first and looks second, so a drain goes in below the pretty stone. A driveway needs packing stone for strength and locking stone for the surface, which is why the good ones have two layers.

Ground and traffic change the answer every time. Soft clay and a loaded truck ask more of a stone than firm soil and a small car.