Pea Gravel Calculator

How much pea gravel you need

Pea gravel is the small, smooth, rounded stone about the size of a pea that shows up on walkways, patios, playgrounds and around plants. It is sold by the ton in bulk or by the bag at a home center, and both are priced off the same two things: the volume you need and the depth you spread it.

Volume is the area times the depth. Area is length times width in feet, and depth is in inches, so the only tricky part is keeping the units straight. The calculator handles that, and it also converts to cubic yards and tons so you can compare a bulk quote against a stack of bags.

Pea gravel weighs about 100 pounds per cubic foot, or roughly 1.35 tons per cubic yard. That single number is what turns a volume into a weight, and it is the reason a job that looks small can still mean a pickup load of stone.

Pea gravel is a surface material, not a structural one. It sits on top of compacted soil or a base and it does not carry a car the way a proper driveway base does. That is why it suits paths, patios and play areas, and why it is a poor choice for a driveway on a slope.

The math behind the gravel estimate

Start with the area: length times width, both in feet. A 20 by 10 foot path is 200 square feet. Multiply by the depth in inches, then divide by 12 to get cubic feet. At 2 inches, 200 times 2 divided by 12 is 33.3 cubic feet.

Divide cubic feet by 27 to get cubic yards, so 33.3 is 1.23 cubic yards. Multiply cubic yards by 1.35 to get tons, which is 1.67 tons. That weight is what a bulk yard will quote you, and it is what a delivery truck will drop in your driveway.

Bags work the same way. A standard bag holds 0.5 cubic feet, so 33.3 cubic feet is about 67 bags. Bags cost more per ton but you can carry them yourself and spread them a few at a time.

Colorado State University Extension notes that gravel mulch should go on at 3 to 4 inches deep to suppress weeds and hold soil moisture, which lines up with the depths above.

Worked example: a 20 by 10 foot path

Say you are covering a 20 foot by 10 foot path with 2 inches of pea gravel. The area is 20 times 10, which is 200 square feet.

Volume is 200 square feet times 2 inches, divided by 12, which is 33.3 cubic feet. In cubic yards that is 33.3 divided by 27, or 1.23 cubic yards.

Weight is 1.23 times 1.35, which is 1.67 tons. Round up and order 2 tons, because a little extra beats a short load and stone settles into the soil. In bags, 33.3 divided by 0.5 is about 67 half-cubic-foot bags, which is more than most people want to carry, so bulk is the smarter buy at this size.

At $45 a ton the material is about $75. Add a roll of woven weed barrier and some steel edging, and the whole path comes in under $150 in materials for a weekend of work. Compare that to the same path in pavers, which can run several times more once you add the base and the labor.

How deep to spread pea gravel

Depth is where most projects go wrong, either too thin to cover the soil or so deep the stone shifts underfoot. Match the depth to the job.

For a decorative bed around plants, 2 inches hides the soil and looks finished. For a walkway, 3 inches gives a stable surface that will not scuff down to dirt. For a play area, 4 inches or more cushions a fall, and some play structures call for 6 inches. For soft or uneven ground, add an inch to make up for what sinks in.

Pea gravel is rounded, so it does not lock together the way crushed stone does. That makes it comfortable underfoot and good for bare feet, but it also means it moves. On a slope, it will roll downhill, so use edging and consider a flatter spot or a different stone.

The Washington State University guide to mulches is a helpful reference for how deep different ground covers should go and how gravel behaves as a permanent surface.

Once the stone is down, top it up every year or two. Pea gravel sinks into soft ground and gets kicked into the grass, so most paths lose about an inch of depth over a couple of seasons. A bag or two brings it back to the level you want.

Bags, bulk and cost

Bulk is almost always cheaper per ton. A ton of pea gravel in bulk runs about $30 to $70 delivered, while the same ton in 0.5 cubic foot bags can cost $200 or more. The catch is that bulk arrives as a pile in your driveway and you move it yourself, unless you pay for placement.

Bagged stone makes sense for small jobs: a border, a planter, a spot under a downspout. For anything over about 10 square feet at 3 inches, bulk wins on price and on your back, because you are shoveling 50 pound bags instead of a pile.

Add the extras to your budget. A weed barrier runs about $0.20 a square foot, and steel or plastic edging runs a few dollars per linear foot. Both keep the stone where you put it, and both cost far less than redoing the job next spring.

Ask the yard whether the price is per ton or per cubic yard, because those are different numbers. A ton is about 0.74 cubic yards, so a quote of $45 per cubic yard is not the same as $45 per ton. Confirm the unit before you compare two sellers.