River Rock Calculator for Beds, Borders and Dry Creeks
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Rock goes into a Virginia bed for one of two reasons, and the ground tends to pick which. On flat Coastal Plain lots where water sits close to the surface, a stone bed is usually taking runoff somewhere useful. On a Piedmont slope with red clay under the grass, it is holding soil in place that would otherwise wash into the lawn by August. The quantity arithmetic is the same either way. The depth is not, and that is where most orders go wrong.
The two windows most rock beds around here get built in
Spring is the first, once the clay has drained enough to walk on without leaving prints and frost is out of the ground in the northern counties and the mountains. Autumn is the second, and on the Bay and the tidal rivers it is worth waiting until the tropical storm season has passed rather than laying a fresh bed into it.
Midsummer work is possible and mostly a question of heat rather than ground. What holds jobs up is water: saturated clay, a low coastal lot that has not dried out, or frozen ground at elevation. Order the stone for a week you can actually spread it in, because a rock pile is the least convenient material to leave sitting on a lawn.
Measuring a border that follows the house, and a creek that does not
Decision criterion: does the shape have parallel sides?
- A foundation border or a straight bed has them. Run the tape along the wall for the length, then take the width at three or four points and enter the average.
- A dry creek does not. Walk the centerline for the length, measure the top width at the head, the middle and the outfall, and average those.
- A curved or kidney-shaped bed gets broken into two or three rectangles that between them cover the shape. Bulges and pinches tend to cancel out.
Measure to the inside face of any edging. The stone stops there, and a strip of steel or timber around a 40 ft border can otherwise add a yard of area that never gets filled.
A layer about twice the thickness of the stone in it
A rock layer covers the ground when it is about twice the thickness of the stone in it. Thinner than that and fabric shows through between the pieces, which reads as a shortage but is really a depth problem.
- 3/4 to 1 inch stone: 2 inches. Anything finer is rounded 3/8 inch stone, sized on its own page.
- River Rock at 1 to 3 inches: 3 to 4 inches.
- Large River Rock at 2 to 4 inches: 4 to 5 inches.
With the depth settled, the form takes the rest. Rectangle wants a length and a width in feet. Circle wants a diameter in feet, which suits a ring around a tree or a splash basin. Multiple areas holds up to five entries, so a bed that turns a corner goes in as two legs rather than two visits to the page. Depth (inches) accepts 0.25 up to 24. The material select fixes the weight conversion, the tick box marked for compaction and spillage adds 5 per cent unless you untick it, and the results come back as cubic yards, tons and cubic feet, with Email my quote sending the set to you.
Why a ton of rounded stone makes a smaller pile than people expect
River rock is published on this site at about 2,700 lb a cubic yard, which is 1.35 tons. Turn that around and a ton occupies roughly three-quarters of a cubic yard, so a delivered ton looks modest beside the same weight in soil or mulch.
Cubic yards are the figure to picture, because they tell you what the bed holds and how much of the drive the pile will take. Tons are what the order is written in. Cubic feet earn their place on small work, where a splash pad under a downspout comes to two or three cubic feet and a yardage figure is all decimal point.
Three beds, measured and converted
Hypothetical jobs, not customer work, with the arithmetic shown.
A dry creek from the downspout to the ditch
Thirty-eight feet long, averaging 3.5 ft across the top, so 133 square feet. At 4 inches for 1 to 3 inch stone: 133 x 4 / 12 = 44.33 cubic feet. Divide by 27 for 1.64 cubic yards, and at 1.35 tons a yard that is 2.22 tons. The 5 per cent tick moves it to 2.33. Order 2.5 tons and set the largest pieces a third of their depth into the ground so they look placed rather than tipped.
A front bed that turns the corner of the porch
Two legs, 18 by 4 ft and 12 by 5 ft, entered as two areas: 72 plus 60 is 132 square feet. At 3 inches: 132 x 3 / 12 = 33 cubic feet, 1.22 cubic yards, 1.65 tons. That works out at about 80 square feet to the ton, which is the coverage figure to sanity-check any 3-inch job against.
A foundation border on a flat Tidewater lot
Forty-six feet by 2.5 ft is 115 square feet. At 2 inches of 3/4 to 1 inch stone: 115 x 2 / 12 = 19.17 cubic feet, 0.71 cubic yards, 0.96 tons. Call it a ton, slope it away from the wall, and let the roof runoff track along it instead of into the grade.
Where the surplus goes, and where it just sits
Round up on anything with a visible front edge. The extra half ton doubles the depth along the strip people walk past, which is the part that thins first. Round down on splash pads and small infills, since a few cubic feet is a wheelbarrow and a half.
Under a decorative bed, put down non-woven fabric and pin it before the stone. Where the stone is carrying water rather than dressing the ground, Drain Rock wrapped in fabric does that work, and it is a separate entry on the form at its own depth. If you are weighing stone against a bark covering for the same bed, the mulch calculator converts the identical measurements at its own much lighter weight. When the tonnage looks right, open the product page, set your quantity and date, and delivery is arranged at checkout by ZIP code, which is what how delivery is arranged covers.
Common questions
The bed wraps around the corner of the porch. Do I have to run the calculator twice?
No. Switch to multiple areas and enter each leg as its own rectangle, up to five of them. Legs of 18 by 4 ft and 12 by 5 ft at 3 inches come back as one total of 1.22 cubic yards and about 1.65 tons rather than two figures to add up by hand.
My edging sits outside the bed. Do I measure to it or to the planting?
Measure to the inside face of the edging, because that is the line the stone fills to. On a long border the difference is real: an extra 2 inches of width along 46 running feet is nearly 8 square feet of stone that gets tipped and never placed.
The bed is 5 inches deep to the fabric. Does decorative stone go all the way down?
Only where it is doing a job. A decorative layer wants about twice the stone thickness and no more, so 3 to 4 inches of 1 to 3 inch rock is the visible course. If the bed is also a drainage line, size the stone underneath as its own entry at its own depth, and keep that stone wrapped in fabric rather than laid on top of it.
There is not a straight edge anywhere on this bed. What goes in the length and width boxes?
Overlay two or three rectangles on it so that what they overshoot on the curves roughly matches what they miss. Enter those under multiple areas. Rounded beds tend to be shallowest at the edges, so a rectangle that runs slightly wide usually balances out against the depth it loses there.
The old bed has thinned and the fabric is showing through. What depth do I enter?
The depth that is missing, not the finished depth. Rake the existing stone level, probe it in four or five places against a straightedge, and enter the shortfall, which is usually 1 to 1.5 inches. Topping a bed back up is a depth job rather than an area job, so the square footage stays as it was.
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