Stone Calculator for Footing Drains, Trenches and Bedding Layers

Two tools on this site look like they do the same thing. This one is for stone bought by a grade number and buried in a layer with a job to do: drainage, bedding, backfill, a construction entrance. The gravel calculator is for the surface you drive and walk on. The difference matters because the grade decides the tonnage before your measurements do, and because putting the wrong one in a trench is a mistake that only shows up in the second wet winter.

A 48-foot footing drain on a Middle Tennessee hillside

Take a hypothetical house sitting into a slope, with water arriving at the uphill wall every time a storm comes through. The drain runs 48 feet along that wall, the trench is 18 inches wide, and the stone goes 20 inches deep around a perforated pipe.

Width in feet is 1.5, so the area is 48 x 1.5 = 72 square feet. Depth is 20 inches: 72 x 20 = 1,440, divided by 12 gives 120 cubic feet. Divided by 27 that is 4.44 cubic yards. Washed #57 stone weighs about 2,800 lb a cubic yard, which is 1.40 tons a yard, so the order is 6.22 tons, or 6.53 with the five percent ticked.

The pipe takes up less of that trench than people expect. A 4 inch pipe over 48 feet occupies about 4 cubic feet, roughly a wheelbarrow and a half out of 120, so ignore it and let the surplus go to the outfall end where the last few feet always look thin. Non-woven fabric goes in the trench before the stone, or silt off the clay closes the voids and you have built a buried sponge.

Trench width in the width field, and a depth that stops at two feet

The tool takes Rectangle, Circle or Multiple areas, and it totals up to five pieces in one go, which is how a wall drain, a downspout run and a soakaway become a single order.

For a trench, the length is the run and the width is the trench, both in feet. Convert inches to decimals: 18 inches is 1.5, 9 inches is 0.75. Depth goes in as inches and the field accepts 0.25 up to 24, which is the one place a drainage job can outgrow the form. A trench deeper than two feet gets split into two entries at half its depth each, which is also how you would place and settle the stone anyway.

Choose the grade in the material list, because the tons figure comes from that stone's own weight. Leave the box for five percent extra ticked if you want the margin. The result gives cubic yards, tons and cubic feet together, and there is an email button if you want the numbers off the screen.

The same trench in four grades, four different tonnages

That 4.44 cubic yards does not move. What moves is the weight.

Clean washed sizes are lighter for the same space because the gaps between the pieces stay open. That open space is the whole reason a drain works, and it is also why the heavier materials on that list belong somewhere else.

Rounding up on stone that ends up under something else

Angular clean stone settles by around five to ten percent once traffic or backfill gets on it, which is what the five percent box is nodding at. Blends with fines in them tighten further, by design.

The practical rule is about access rather than arithmetic. Stone that ends up under a slab, under pipe, behind a wall or at the bottom of a trench is stone you cannot top up later without taking something apart, so round the first order up. A half ton that arrives on its own after the trench is closed means a second delivery for the sake of two wheelbarrow loads. Stone going on top of something, like a path surface or the finish course on a pad, can be ordered closer to the mark.

Grade numbers, and which ones drain instead of lock up

The numbering runs backwards from how people expect: the smaller the number, the bigger the rock. #4 is the largest of the common sizes at roughly 3/4 to 1-1/2 inches, #57 runs 3/16 to 1 inch, #67 comes in finer at 1/4 to 3/4, #8 sits around 3/32 to 3/8 inch, and #89 runs from 3/8 inch down through fines. Screenings are dust and small chips together, which is why they screed flat and set firm under flagstone and pavers. Railroad ballast is heavy angular 1 to 2.5 inch rock for farm tracks and equipment pads that cross wet ground.

Past the numbers there are only two families. Washed clean stone leaves voids, so it drains: #57 and #67 in footing drains, around pipe, behind retaining walls. Material with fines in it compacts and locks, so it carries load: crusher run and graded base under lanes, pads and paver bases. Swap them and both jobs fail. Crusher run in a footing drain silts up and holds water against the wall, and clean stone under a paver base keeps shifting because nothing binds it.

A construction entrance shows the coarse end in use. A strip 36 by 14 feet at 6 inches of #4 crushed stone is 504 square feet, so 504 x 6 = 3,024, divided by 12 is 252 cubic feet, divided by 27 is 9.33 cubic yards, and 13.5 tons at 1.45. Big angular rock locks under a loaded truck while letting water through, which is exactly what the mud at a gateway needs.

If a plan or a permit names a gradation, follow the plan. Where a supplier ticket says something like 3/4 clean, that is usually the same material as #57 under another name.

Once the tonnage is settled, open the product page for the grade you picked, set the quantity and choose a delivery date. Delivery is arranged at checkout from the ZIP code you enter, and the driver needs firm, clear ground to tip on.

Common questions

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