Flagstone Calculator
Find how much flagstone you need for a patio, walkway or stepping stones. Enter the area and thickness to get the tons needed, based on typical coverage per thickness.
Flagstone needed
Coverage per ton varies by stone type and thickness; confirm the exact rate with your supplier for a large order.
How to calculate flagstone
Flagstone is irregular in shape, so it is not sold by the piece like pavers; it is sold by weight, with a typical coverage rate per ton that depends on the stone's thickness. Thinner stone covers more area per ton because there is simply less material per square foot. The calculator starts from your area in square feet (length × width, or π × radius² for a circle), divides by the coverage rate for your chosen thickness, and adds your waste allowance. The formula is tons = area (ft²) ÷ coverage rate (ft² per ton) × (1 + waste %).
As a reference, 1 inch flagstone covers roughly 110 to 130 square feet per ton, 1.5 inch covers about 80 to 100 square feet per ton, and 2 inch covers around 60 to 75 square feet per ton. These rates vary by stone type (bluestone, flagstone sandstone, slate and quartzite all differ slightly in density), so treat the result as a solid planning estimate and confirm the supplier's exact rate before a large order.
Choosing a thickness
Thinner flagstone (1 inch) is lighter and cheaper per square foot but is best mortared over a solid concrete slab rather than dry-laid, since it can crack under point loads on a soft base. 1 to 1.5 inch stone is the common middle ground for a dry-laid patio over a compacted gravel and sand base. Individual stepping stones set into a lawn or garden bed are usually the thickest, 1.5 to 2 inches, so each stone stays stable and does not rock underfoot.
Dry-laid vs mortared
A dry-laid flagstone patio sits on compacted gravel topped with a sand or stone-dust leveling bed, with joints filled with sand or planted with low groundcover; it can shift slightly over time but is simpler to build and repair. A mortared patio sits on a cured concrete slab with the joints grouted, giving a more rigid, formal surface that resists weed growth but is less forgiving of frost heave in cold climates. Either way, size the gravel base with the gravel calculator and a mortared slab with the concrete calculator.
Fitting allowance
Because flagstone pieces are irregular, fitting them together like a puzzle always leaves some unusable trim and gaps along borders and curves, more than a uniform paver layout needs. A 10 to 15 percent allowance is typical; lean toward the higher end for a tightly fitted, hand-selected look or a patio with a lot of curved edges.