A wall is a trapezoid and the order is a weight
Two conversions stand between the wall you have drawn and the ticket at the quarry. The first is shape. A stone wall is almost always wider at the bottom than the top, because the batter is what keeps it standing and what makes it look like a wall rather than a stack. The volume of a battered wall is the average of the two widths times the height times the length, which is less than the base width would suggest. On a wall 24 inches at the base and 18 at the top the average is 21, so using the base overstates the order by 14.3 percent.
The second is packing. Random stone never fills the space it occupies. Between the face stones there are voids and small hearting stones, and on a dry-laid rubble wall the solid rock is commonly 75 to 85 percent of the wall volume. Multiply the volume by that fraction, then by the density, and the tons fall out. Squared ashlar packs tighter than field-run rubble; round cobbles pack worse than either.
| Wall section | Average width | Volume per linear ft, 3 ft high | Tons per linear ft at 80% and 165 lb/cu ft |
|---|---|---|---|
| 18 base, 18 top | 18 in | 4.50 cu ft | 0.297 |
| 24 base, 18 top | 21 in | 5.25 cu ft | 0.347 |
| 24 base, 24 top | 24 in | 6.00 cu ft | 0.396 |
| 30 base, 20 top | 25 in | 6.25 cu ft | 0.413 |
The unit the stone is sold in is the trap
Wall stone comes by the ton. Thin veneer stone comes by the square foot of face, and corner pieces come by the linear foot. Flagging comes by the ton but is quoted in square feet of coverage per ton, which depends entirely on its thickness. Ordering one of those in the units of another is where the money goes.
The face coverage line in the results is there to make the comparison possible: it tells you how many pounds of stone go into each square foot of wall face, which for a two foot thick wall is a much larger number than any veneer product will ever quote. If a supplier gives you a coverage figure in square feet per ton, ask what thickness they measured it at, because that single number decides everything.
What holds the wall up is not on this page
Quantity and stability are different problems. A free-standing dry stone wall stands because of its section, its batter, the through stones that tie the faces together and the care of the person laying it. A wall with earth behind it is a retaining wall, and there the height, the soil type, whatever sits above it, the drainage behind it and any reinforcement decide whether it stays where it was built. Those are engineering questions with local code attached, and no calculator can answer them.
Say the ground behind the wall is holding a driveway or a slope, or the wall is going above waist height, or there is any doubt at all. That is the point to bring in an engineer and the building department before ordering stone. For a segmental block wall instead of natural stone, the retaining wall block calculator counts blocks, caps and drainage stone with the same caveat attached.
Ordering and handling
Order in one delivery if you can, because stone from two different pulls of the same quarry can read as two different colours in one wall. Have the drop point chosen and reachable; loose stone tipped in the wrong place gets handled twice, and stone is the worst material there is to handle twice. Budget the culling honestly, because on random field-run a fifth of what arrives may not be the shape you need where you need it.
For a thin adhered veneer instead of full-bed wall stone, the stone veneer calculator handles the flats and corners split. For the mortar if you are bedding rather than dry-laying, the mortar mix calculator covers the proportions, and for the total weight arriving on site the masonry weight and pallet calculator turns tonnage into trips.
Questions people ask
How many tons of stone do I need for a wall?
Take the average of the base and top widths in feet, multiply by the total height including anything buried, multiply by the length to get cubic feet, take 75 to 85 percent of that as solid rock, and multiply by the stone density. A 20 foot wall 3 feet 6 inches tall overall, 24 inches at the base and 18 at the top, is 122.5 cubic feet of wall, 98 cubic feet of rock at 80 percent, and about 8.1 tons at 165 pounds per cubic foot, or 8.9 tons with 10 percent for culling.
What does building stone weigh per cubic foot?
It depends on the rock. Granite and basalt sit at the high end, around 165 to 180 pounds per cubic foot. Limestone and sandstone are lighter, commonly 145 to 165. Slate, quartzite and fieldstone all fall inside that band somewhere. The quarry or yard knows what theirs weighs and it is worth asking, because a 15 percent difference in density is a 15 percent difference in the order.
Why does the calculator ask for a solid percentage?
Because stone is not concrete. Random shapes leave voids, and on a dry-laid wall those voids are filled with small hearting stone that came out of the same pile rather than with anything you buy separately. If you priced the wall as though it were solid rock you would overbuy. Eighty percent is a reasonable middle for rubble; squared and coursed stone runs higher, round cobbles lower.
Do I need a footing under a dry stone wall?
Traditional dry stone walls sit on a compacted stone foundation in a shallow trench rather than on concrete, because the wall needs to be able to move slightly without cracking. How deep that trench goes and how wide depends on the soil, the frost conditions where you are and the wall itself. That is a design decision, and for anything retaining ground or above modest height it belongs with an engineer and the building department.
How much stone is wasted?
More than on almost any other material, because you are sorting for shape as well as size. Ten percent is realistic on squared and graded stone where most pieces are usable somewhere. On random field-run, 15 to 20 percent is normal and the leftovers become hearting or garden edging rather than being thrown away. Order in one go: a second small delivery of the same stone often does not match the first.