River Rock Calculator: Sizing the Channel the Snowmelt Already Cut
Enter your project dimensions
Every thaw the melt comes off the slope behind the camp, finds the same line across the lawn, and takes a little more soil with it on the way past. Lining that line with stone is the job that brings most people to this river rock calculator.
So take the work in the order you will actually do it. The arithmetic is one stage of five.
Walking the line the water picked out
Go out during a thaw, or an hour after a hard summer rain. The water has already surveyed the lot and it will not change its mind for landscaping.
Mark where the flow starts. Usually a downspout, a culvert outlet on a camp road, or the low corner of a drive. Mark where it needs to end up: the ditch, the treeline, a bank well away from the foundation.
Two things to settle before any measuring.
Is this decoration or is it drainage? Stone slows water and hides bare ground. It does not armor a bank. If spring runoff has been moving cobble-sized material along that line already, size the work on the rip rap calculator instead.
How much soil is over the ledge? Push a bar down in three or four spots. Where granite is 5 inches under the grass, the channel gets built up with low shoulders rather than dug in, and the depth you type is the height of stone you are laying on top.
Pacing a channel that is three widths, not one
Nothing that water cut is a rectangle.
Break it into pieces where the width changes and measure each one in feet: the narrow run at the top, the wider basin in the middle where it slows, the fan at the outlet. The tool adds up to five separate areas into one total, which is what that option is for.
On a curve, pace the length along the middle of the bend, not around the outside of it.
Measure to where the stone will stop. Not to where the grass happens to stop.
Stone size sets the depth, and the depth sets the order
Coverage changes with size, so this decision comes before the numbers rather than after them.
The layer wants to be roughly twice the diameter of the stone. Any thinner and soil or fabric shows through, which reads as a shortage of material when it is really a shortage of depth.
| Stone | Layer depth |
|---|---|
| 3/4 to 1 inch | 2 inches |
| River rock, 1 to 3 inch | 3 to 4 inches |
| Large river rock, 2 to 4 inch | 4 to 5 inches |
Bigger stone therefore covers about half the ground per ton. Sizing up is not a saving.
Where the channel carries real water rather than looking as though it might, drain rock does the work and the decorative stone goes on the visible shoulders.
What the river rock calculator does with three sections
Pick the shape first: rectangle, circle, or multiple areas for up to five pieces totaled together. Length, width and diameter go in as feet. Depth goes in as inches, anywhere from 0.25 to 24. Choose the material, since the weight rides on that choice.
There is a box that adds 5% for compaction and spillage. On a loose decorative bed nothing is being compacted, so untick it unless the drop spot is rough and you expect to lose a wheelbarrow-load in the grass.
Out come cubic yards, tons and cubic feet. Email my quote puts the figures in writing.
Hypothetical channel, 1 to 3 inch stone at 4 inches deep, entered as three areas:
- Upper run, 16 x 3 = 48 sq ft
- Middle basin, 9 x 5 = 45 sq ft
- Outlet fan, 13 x 4 = 52 sq ft
- Total area 145 sq ft
- 145 x 4, divided by 12 = 48.33 cu ft
- 48.33 / 27 = 1.79 cu yd
- 1.79 x 1.35 = 2.42 tons
Round that to two and a half tons and the extra doubles the depth at the outlet, which is where thin cover shows first.
Fabric, pins, then the anchor stones
Bare soil takes stone downward a little every year, and weeds come up through the gaps.
Lay non-woven fabric and pin it before a stone goes down. The one exception is a run actively carrying water, where the fabric wraps around the stone rather than sitting under it.
Set the largest pieces first and bed them about a third of their height below grade. Stone sitting proud on the surface looks tipped out. Stone set into the ground looks as though the water put it there.
Rinse the bed with a hose when you have finished. Quarry dust is what you are looking at until then, and the color comes up once it is off.
Come autumn, move leaves off with a blower on a low setting. A rake throws stone into the lawn, and the mower finds it in June.
Two and a half tons is a smaller heap than you are picturing
River rock runs about 2,700 lb per cubic yard on this site, which is 1.35 tons. Turn that around and a delivered ton is only about three-quarters of a yard.
The three outputs answer three different questions. Cubic feet is the hole. Cubic yards is the pile. Tons is what goes on the truck, and what the stone is sold by.
Checking it on paper: area in square feet, times depth in inches, divided by 12, divided by 27, gives cubic yards. Times 1.35 gives tons.
When the figure looks right, open the product page, set a quantity and a date, and delivery is arranged at checkout from your ZIP code. The truck needs firm ground and clear room to tip. Other materials for the same job have their own entries among all the calculators, and the delivery page covers access before a load is booked.
Common questions
Where should the pile go if the channel runs the length of the lot?
Somewhere firm, within wheelbarrow distance of the far end, and off the lawn. Stone is easier to move downhill than up, so put it at the high end of the run if the truck can reach it. Two and a half tons sits in roughly an 8 foot circle about 3 feet high, so allow for that before picking the spot.
The result shows yards and tons for the same stone. Which one am I buying?
Tons. The yardage is there so you can picture the heap and check it against a quote written in yards. One yard of river rock is 1.35 tons, so a yard-based figure multiplied by 1.35 gives the same number.
Do I enter the depth as it lands, or after it has settled in?
As it lands, loose. Decorative stone is raked level rather than compacted, and it beds down maybe a quarter of an inch. That is why the 5% box, ticked by default, can come off on this page.
A round tree ring, not a channel. What goes in the diameter box?
The widest distance straight across the ring, in feet, trunk included. An 11 foot ring at 3 inches works out at 95.0 square feet, 23.8 cubic feet, 0.88 yards and 1.19 tons. Keep the stone itself back off the bark.
Can I check the tons without opening the page again?
Yes, and it is worth doing once. Take square feet, multiply by the depth in inches, divide by 12, divide by 27, then multiply by 1.35. If your answer and the screen disagree, one of you has the depth in feet.
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