Stone Calculator for Drains, Trenches and Pads
Enter your project dimensions
Most people land on a stone calculator with a wet corner in mind. A footing that seeps in April, a yard that ponds where the meltwater cannot get through still-frozen ground, a hollow by the shed that is soup for three weeks and dust in July. That job has a season: the trench cannot be opened until the frost is out and it wants closing well before the ground shuts again in November. Everything below assumes you are working inside that window.
Trench season runs from the end of the thaw to the first hard freeze
The drainage problem announces itself in March and April, when snowmelt sits on ground that is still frozen a foot down. That is the diagnosis stage, not the digging stage. Clay near Green Bay, the Fox Valley and the Lake Superior shore stays greasy for weeks after the surface looks workable, and sandy ground in the Central Sands is open far sooner.
- Mark the wet ground while it is wet. Flags in April save guessing in June.
- Dig once the trench walls will stand without smearing.
- Backfill and finish before the first hard freeze, because a half-open trench collects the winter.
- On a steep coulee slope, plan the outfall before the trench, not after.
Measuring a trench that follows the fall of the ground
A drain is a long thin box. Length is the run of the trench, width is the width of the cut in feet rather than inches, and depth is the stone, not the excavation. Two habits keep it honest:
- On a slope, measure the distance along the ground. That is the surface the trench follows, and it is longer than the flat distance on a plan.
- Do not subtract the pipe. A four-inch line through a thirty-foot trench displaces a fraction of a yard, and the remainder goes in at the outfall.
For a pad, length by width is enough, taken to where the stone stops and not to the building line.
Setting the stone calculator up for a long thin trench
- Shape. Rectangle, circle, or multiple areas, up to five summed in one result. A dry well goes in as a diameter.
- Size. Length and width in feet, or the diameter in feet. A 16-inch trench is 1.33 feet wide.
- Depth. Inches, 0.25 to 24. Deeper than two feet, run it as two passes and add them.
- Material. Twelve graded products, from 3/8 inch chips up to 2.5 inch railroad ballast. The choice sets the weight.
- Extra. The optional tick box adds five percent for compaction and spillage. It is on by default.
- Result. Cubic yards, tons and cubic feet, with the quote emailable to you.
Why Screenings come out heavier than the same yardage of #57
Most crushed grades sit at roughly 2,800 pounds to the cubic yard, which is 1.40 tons. Screenings, the local name for stone dust, run nearer 2,900, about 1.45 tons, because the fines fill what would otherwise be voids. So do #4 stone and railroad ballast. Base material with the fines retained is heavier again at around 3,000 pounds, and rip rap is the heaviest thing on the list at about 3,100.
The volume never moves. Change the grade and the yardage on screen stays exactly where it was while the tonnage steps up or down. That is the whole reason the material select exists.
Checking it by hand takes four steps: square footage, then the depth in inches divided by twelve and multiplied through for cubic feet, then a division by twenty-seven for yards, then the yards multiplied by the figure for your grade.
Forty-four feet of footing drain, then a Screenings cap on the shed pad
Hypothetical jobs, worked through so the arithmetic is visible.
The footing drain runs 44 feet along the foundation, the cut is 16 inches wide, and the stone stands 14 inches deep over the pipe. Sixteen inches is 1.33 feet, so the area is 58.7 square feet. Fourteen inches is 1.17 feet, giving 68.4 cubic feet, which is 2.54 cubic yards. At 1.40 tons to the yard that is 3.55 tons of #57 stone. Wrap the trench in non-woven fabric before the stone goes in, or silt fills the voids and the drain stops draining.
The shed pad is 12 by 16 feet and takes a 2-inch cap of Screenings over a compacted base. That is 192 square feet, two inches is a sixth of a foot, so 32 cubic feet, or 1.19 cubic yards. At 1.45 tons to the yard the cap is 1.72 tons, and 1.80 with the five percent ticked.
Graded stone here, loose drive gravel there
The two calculators overlap and the difference matters at the order line.
- This page is for graded, specified material: #57, #67, 3/4 inch crushed stone, 3/8 inch chips, #4, railroad ballast and Screenings. It is the page to use when a plan, a permit or an inspector names a grade.
- The gravel calculator is for the surface you drive or walk on, where the buyer is choosing by job rather than by grade.
- Clear stone, the Wisconsin term for crushed stone with the fines screened out, stays open so water moves through it. That is drainage material. Material with the fines left in packs tight and carries load. Putting either in the other one's place is the most expensive mistake on this page: fines in a French drain clog it, and clean stone under a driveway never stops moving.
The half ton you keep back for the outfall
Angular stone rolled under traffic settles five to ten percent, so a compacted layer eats more than it looks like it should. The five percent box covers ordinary settling and spillage. Anything engineered should be ordered to its specified compacted depth instead.
- Tick the five percent for anything rolled or driven on.
- Round up rather than down. A trench standing open while a half-ton top-up is arranged is worse than the surplus.
- Keep the remainder for the outfall, the splash pocket or the low corner.
- Order the grade the plan names, then check what it is called here before you check out.
Set your tonnage and a delivery date on the product page. Delivery is arranged at checkout by ZIP code, and the truck needs a firm spot with clear overhead to tip on, well away from an open trench. Grades you are not sure about can go through the contact page with the line item copied out.
Common questions
Is five percent enough on a trench that will be tamped in lifts?
For a drain, yes, and often it is more than you need, because clean stone in a wrapped trench is not compacted hard. For a pad that gets rolled, treat the five percent as spillage cover and add your own rounding on top: angular material settles five to ten percent under traffic, and that comes out of the finished depth rather than out of the tonnage.
The drain line falls from the house down toward the ditch. Which length goes in the box?
The length along the slope, measured with a tape laid on the ground. A plan view understates a falling run, and on a coulee grade the difference over a hundred feet is real stone. Depth is measured square to the trench bottom, not vertically.
The apron by the shed doors bends round toward the well head. Can multiple areas take that in one go?
Yes, as two rectangles with the bend cut at the inside corner so the overlap is counted once. Enter both and the tool returns a single yardage and tonnage. It also lets you give the apron a heavier depth than the strip to the well, which is usually what the job wants.
A row of cobbles will edge the finished stone bed. Does that strip go into the width?
No. Measure to the inside face of the cobbles, because that is where the graded stone stops. The cobbles themselves are a decorative order sized separately, and mixing them into one entry gives a tonnage that is wrong for the bed and wrong for the edging.
The pad needs a packed layer under a clean stone top. Does that go through twice?
Twice, at two depths and two grades. Run the base at its compacted depth with the base weight, then run the top course at two or three inches with the clean stone weight, and order the two tonnages separately. One entry covering both layers would apply a single weight to material that does not share one.
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