Stone Calculator for French Drains, Backfill and Pipe Bedding
Enter your project dimensions
The trench is open in front of you and the spoil is on a tarp, so you can see exactly what you are dealing with: a foot of broken brown shale, then a clay seam that has been holding water since the last thaw. That is the job this stone calculator is sized for. Read the run with a tape, read the width across the bottom, decide how much of the depth gets stone rather than soil, and the tool returns cubic yards, tons and cubic feet for the graded product you select.
What gets measured when the hole is a trench and not a rectangle
A trench is a rectangle turned on edge. Length runs along the pipe, width is the cut across the bottom, and the depth box wants the stone zone only. A 24-inch trench capped with 6 inches of soil and sod is an 18-inch stone entry, and typing 24 buys a third more than the trench will hold.
Drain lines rarely run straight. Where a line turns at a downspout or bends round a porch footer, use the multiple areas option and enter each straight leg on its own, measured from the end of the leg before it so the corner is not bought twice. The tool holds five pieces and totals them.
Backfill behind a wall is measured the same way: the wall length, the width of the stone zone behind the block, and the height the stone rises up the back of the wall.
How deep stone sits over a 4-inch pipe on a wet clay line
The depths that go in the box change with what the layer does. A finish course over an existing surface runs 2 to 3 inches. A base layer takes 4. Pipe bedding is usually 6 inches of #67 under and around the pipe. A French drain wants 12 inches of clean stone or more, and a wall backfill zone can run 24.
Example only. A 40 ft drain line along the uphill side of a garage, cut 12 inches wide, filled with 18 inches of 2B stone and capped with soil.
- Area: 40 x 1 = 40 sq ft
- Depth: 18 in divided by 12 = 1.5 ft
- Volume: 40 x 1.5 = 60 cu ft
- Cubic yards: 60 divided by 27 = 2.22 yd3
- Tons at 1.40: 2.22 x 1.4 = 3.11 tons
The same run ends at a 6 ft dry well 24 inches deep. Choose the circle shape, enter 6 as the diameter, and the area comes out at 3.1416 x 3 x 3 = 28.3 sq ft, which is 56.6 cu ft, or 2.09 yd3, or 2.93 tons. Entered together as two areas, the job reads 4.32 yd3 and 6.0 tons.
Why a yard of screenings outweighs a yard of 2B
The tool works out volume from your measurements first, then multiplies by the published weight of whatever is selected in the material list. Those weights are approximate and they are not the same across the graded products. The clean grades, 2B, #57 and the finer #67, all run about 2,800 lb per cubic yard, or 1.40 tons. Screenings and the coarse end, #4 stone and railroad ballast, sit near 2,900 lb, or 1.45. Crusher run and 2A modified reach about 3,000 lb, or 1.50, because the fines fill the gaps the clean grades leave open. Armor stone is heavier still at roughly 3,100 lb, or 1.55.
That spread matters on a big backfill. A 24 ft wall with an 18-inch stone zone carried 24 inches up the back is 36 sq ft by 2 ft, which is 72 cu ft, or 2.67 yd3. In clean stone that is 3.73 tons. In screenings the same hole reads 3.87, and in armor stone 4.13. The hole did not change; the material did.
How much over to order on a drain you are about to bury
The tick box on this page reads "add 5% extra for compaction and spillage", and it is the only allowance the tool applies. It covers the stone that never leaves the tarp and the ordinary settling of a spread layer. Clean angular stone typically loses 5 to 10 percent of its loose height once traffic works over it, so on a construction entrance or an equipment pad, tick the box and round the order up as well.
Two habits keep a trench order honest. Size the quantity from the trench rather than from the pipe, since a 4-inch line across 40 ft displaces roughly 0.13 yd3, less than a couple of wheelbarrows. And wrap the trench in non-woven fabric before the stone goes in, because soil washing into the voids is what stops a drain working, not a short load.
Clean stone or something with fines: which grade the trench takes
The products here fall into two camps, and mixing them up is the expensive mistake on this page. Washed clean stone stays open so water can move: #57 stone and 2B are the same 3/4 inch size under two names, #67 stone is a touch finer for pipe bedding, and 1B stone is the small chip for joints and finish layers. Anything with fines in it, including 2A modified, compacts into a dense layer for bases and will hold water in a drain instead of passing it.
Where a plan, a permit or a municipal detail names a gradation, order that gradation. Pennsylvania material is specified under PennDOT Publication 408 sizing, and the older yard names run alongside the numbers: 2B is the #57 size, 1B is the #8. That is how stone is described and sold here, not a certification anyone holds.
Stone calculator or gravel calculator: which page sizes your load
Stay on this page when a size is named. If the order line reads a number, a gradation from a drawing, or a bedding or backfill product, this tool is the right one. Go to the gravel calculator instead when the job is a surface people walk or drive on and the choice is between families rather than grades, such as a drive top course or a decorative bed. Base stone for a lane or a pad belongs in the road base calculator, and bank and ditch armor in the rip rap calculator, which runs a heavier weight.
With a tonnage in hand, open the product page for the grade you sized and set the quantity and date there. Delivery is arranged at checkout from your ZIP code, and the truck needs firm ground with room to back in and tip clear of the open trench. Photograph anything already in the ground that you cannot name and send it through the contact page.
Common questions
Is the depth box asking for loose stone or the finished level after it settles?
Enter the finished depth you want the layer to hold once it is in place. In a drain that is the height of stone in the trench after raking, not the heaped pile you tip in. Clean angular grades lose a little height as they settle, which is what the five percent tick box is there for.
The dry well at the end of the line is round. What do I type in?
Switch to the circle shape and enter the diameter straight across the widest point, not the radius. A 6 ft ring at 24 inches deep works out at 28.3 sq ft, 56.6 cu ft, 2.09 cubic yards and about 2.93 tons of clean stone. If the trench feeds it, enter both as separate areas and read one total.
The number looks low for the size of the trench. How do I test it on paper?
Multiply length by width for square feet, divide the depth in inches by 12 and multiply through for cubic feet, then divide by 27 for cubic yards and multiply by the weight of the grade you picked. If your figure and the screen disagree by a factor of twelve, the depth went in as feet when the box wants inches.
I switched from #57 to screenings and the tons moved without me touching a measurement. Which figure do I order to?
The one for the material actually going in the hole. Volume stayed the same, weight did not: clean stone is quoted near 1.40 tons per yard and screenings near 1.45, so the heavier grade returns a heavier ticket for an identical trench.
Does ticking five percent cover a trench bottom that is soft?
No. It covers spillage and normal settling. Ground that has been wet all spring will take the first few inches of stone into itself, and no percentage box can measure that. Fabric under the stone is the usual answer, with a little extra ordered on top of it.
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