Stone Calculator: Graded Stone by the Spec Number
Enter your project dimensions
Dig a test hole at the low corner of the house in April and the ground will tell you most of what you need. Wherever the sides go dark and stay dark, that is the level water is sitting and moving at, and on the flat lake-plain clay of the southeast it is usually higher than anyone expects. That measurement, rather than a chart, is what belongs in the depth field of this stone calculator when the trench is for drainage.
Digging to the wet line, then entering that depth
Drainage stone is sized by the volume of the trench, so the trench has to be decided first. Carry the stone from the bottom of the excavation up past the wet line by several inches, which on slow-draining clay usually means a deeper section than the same detail would need in the sandy outwash on the west side.
Frost is the other reference point. The residential code puts frost depth at 42 inches, and local building officials can ask for more where winters are colder. Drains and beds are not footings and do not have to reach that, but water held in a shallow stone layer over clay is what lifts a slab edge or a step by March.
A worked example, hypothetical but typical. A footing drain runs 52 feet along one wall, the trench is 16 inches wide, and the stone stands 12 inches deep over the pipe:
- 52 x 1.333 = 69.33 square feet
- 69.33 x 12 / 12 = 69.33 cubic feet
- 69.33 / 27 = 2.57 cubic yards
- 2.57 x 1.4 = 3.60 tons
- with the 5 percent allowance ticked: 2.70 cubic yards, 3.78 tons
Order three and three-quarter tons of #57 stone and put the balance at the outfall. Do not deduct the pipe: a four-inch line takes up about 0.17 of a cubic yard over that run, which is less than the rounding.
Entering a trench in the stone calculator: length one way, width the other
Three shapes are offered. A rectangle takes the trench length as the length and the trench width as the width, which is the only part of this that catches people out. A circle takes one diameter, for a drywell or a ring around a downspout. Multiple areas totals up to five pieces, so a drain along two walls and a splash pad at the corner come back as one figure.
Horizontal measurements go in feet and depth goes in inches, from 0.25 to 24. Pick the product in the material list so the tonnage uses its own weight, then decide on the optional checkbox that adds 5 percent for compaction and spillage. It starts ticked, and nothing is added if you untick it. Cubic yards, tons and cubic feet appear together, and the estimate can be emailed rather than transcribed.
Why 2,800, 2,900 and 3,100 pounds share one dropdown
Square feet times depth in inches, divided by 12, gives cubic feet. Divide by 27 for cubic yards. Multiply by the weight of the grade you chose for tons, and the grades do not weigh the same.
Most washed grades, which covers #57, #67 and 3/4 inch stone as well as the smaller #8 and #89 chips, run about 2,800 lb a cubic yard, or 1.40 tons. Stone screenings and the #4 end of the range, including railroad ballast, come in around 2,900 lb, or 1.45. Dense-graded 21AA sits at about 3,000 lb, or 1.50, and rip rap at roughly 3,100 lb, or 1.55. Those are the site's own approximate published figures.
Coverage is the same arithmetic in reverse. At 1.40 tons a yard, one ton spreads about 116 square feet two inches deep, 77 at three inches, 58 at a four-inch base and 39 at six.
Smaller number, bigger rock: #4 down through #89
- #4 is 3/4 to 1-1/2 inches, for heavy drainage, trench bottoms and construction entrances onto soft ground.
- #57 is 3/16 to 1 inch, the general drainage, driveway and concrete grade, and the one most Michigan French drains are built from.
- #67 is finer at 1/4 to 3/4 inch, which is why it goes around pipe.
- #8 and #89 run from about 3/8 inch down, #89 carrying fines with it, and both suit paver joints and finish layers.
- Screenings are dust and small chips together, which screed into a firm bed under flagstone and pavers.
- Railroad ballast is heavy angular stone of 1 to 2.5 inches, used where wet ground has to carry weight, including pole barn pads.
If the plan or the permit names a gradation, follow the number rather than the description. Local names travel: 3/4 clean and #57 are usually the same stone, and 57s is the same again.
Clean stone drains, fines pack, and swapping them ruins both
Everything on this page falls into one of two camps. Washed clean grades leave open voids that water moves through, which is what a drain needs. Dense-graded material carries fines that tighten under compaction, which is what a base needs. Put crusher run in a French drain and the fines silt it up. Put #57 under a drive and it keeps shifting.
Size the base layers on the tools built for them: 21AA and road base for pads and lanes, and the gravel tool for driveway and pad quantities and for pea stone. This page is for the graded stone you are ordering by its number.
Two more worked figures to check your own against. A 34 by 14 approach onto soft ground, six inches of #4, is 476 square feet, 238 cubic feet, 8.81 cubic yards and 12.8 tons. A flagstone bedding course of screenings 1.5 inches thick over a 12 by 14 patio is 21 cubic feet, 0.78 cubic yards and 1.13 tons.
Angular stone settles about a tenth, so 5 percent is a floor
Clean angular stone consolidates roughly 5 to 10 percent under traffic, and dense-graded material more than that. The checkbox covers the lower end of it, which makes it a sensible default rather than a complete answer. Where a drawing specifies a compacted depth, work to that depth and let the allowance sit on top.
Line drainage trenches with non-woven fabric before the stone goes in, so the voids stay open and soil does not wash into them. Where the stone is working as a drain rather than a decorative layer, wrap the stone in the fabric rather than laying the fabric flat underneath it. On the clay of the southeast that detail is the difference between a drain that works for years and one that silts up in two.
Once the tonnage settles, open the product page for the grade you need, set a quantity and a date, and finish at checkout, where delivery is arranged by ZIP code. Leave the truck a firm spot within reach of the trench, because clean stone is awkward to move twice.
Common questions
The drain runs down a slope from the house to the ditch. Do I measure along the ground or level?
Along the ground, since that is the length of trench you are filling. A tape laid on the slope gives the real figure. The depth stays the depth of the stone above the pipe at each point, and if the trench deepens as it falls, average a few readings rather than using the deepest one.
The drain turns the corner of the house. Do I run it as one length or two?
Two, entered under the multiple-areas option. Running it as a single length either double counts the corner or misses it, depending on where you started the tape, and the corner is usually where the trench is deepest.
Does the pipe bedding go the full width of the trench or just under the pipe?
Full width. Bedding stone is calculated on the trench footprint, not on a strip beneath the pipe, because the stone has to surround the line rather than sit under it. Use the trench width in the form and keep the pipe out of the arithmetic entirely.
I need a coarse base and finer stone on top. Is that one calculation or two?
Two, on the same footprint at different depths, changing the material each time. The weights differ between grades, so adding the depths together and running them once as a single material gives a tonnage that matches neither layer.
The area is a curved apron with no straight edge on it. What do I put in?
Take the smallest rectangle that contains it, then estimate what share of that box is actually being stoned, usually two thirds to three quarters, and scale the yardage by that share. For anything closer to a circle, the diameter and the circle option get there in one step.
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