Flagstone Calculator
Plan a flagstone patio or walk: stone in tons by thickness, plus the compacted gravel base and sand bedding underneath it.
Stone by the ton, figured from thickness
Flagstone is quarried, split and sold by weight, so the count runs through density: sound flagging stone (bluestone, sandstone, slate) runs about 160 lb per cubic foot. Multiply the patio area by the stone thickness and that density and you have the weight to order — about 13 lb per square foot for every inch of thickness. Underneath, a proper patio wants the same build as pavers: 4 in of compacted gravel base and 1 in of bedding sand, and both are in the result.
Stone weight = area × thickness × 160 lb per cu ft · Base = area × 4 in of gravel · Bedding = area × 1 in of sand
Example: a 100 sq ft patio in 1 1/2 in stone is 12.5 cu ft of stone — exactly 1 ton, so 1.1 tons to order with the 10% allowance — over 1.24 cu yd of base gravel (1.73 tons) and 0.31 cu yd of bedding sand (0.42 tons).
Irregular or cut stone?
Irregular flagstone is fitted like a jigsaw and the waste allowance pays for the edge pieces that get trimmed or rejected; stay at 10% for a random pattern, 15% if you are picky about color. Cut (dimensional) stone in a grid wastes less and orders closer to the exact figure. Stone is usually delivered on pallets of roughly 1.5 to 2 tons — if your count lands just over a pallet line, dropping the depth of base or accepting the extra pallet for the next project is the supplier conversation to have before delivery day.
For dry-laid work, joints are filled with stone dust or polymeric sand after laying — a bag-count the paver and sand tools can sanity-check from the same area. Mortared flagstone over a slab skips the base and bedding entirely; order the stone only, and mortar from the mortar calculator.
Frequently asked questions
How much does a pallet of flagstone cover?
A pallet runs about 1.5–2 tons. In 1 1/2 in stone that is roughly 150–200 sq ft per pallet; in 1 in stone, 225–300 sq ft. The calculator's tonnage converts directly — divide your total tons by about 1.75 for a mid-estimate of pallets.
Can flagstone go straight onto soil?
It will move, tilt and grow grass in the joints within a season. The compacted gravel base is what keeps a patio flat — it is a third of the project's material for a reason, and skipping it is the classic false economy.
What thickness for a driveway or fire pit area?
2 in minimum where vehicles or a fire pit's heat load bear, over a deeper 6 in base. The calculator counts the stone for any thickness; deepen the base figure by scaling the gravel rows up by half.
Bluestone, sandstone or slate — does the count change?
Barely. Their densities sit within about 5% of the 160 lb per cu ft used here (sandstone a touch lighter, slate a touch heavier) — inside the waste allowance either way.
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