How this calculator works
It multiplies your area by a waste allowance to get the square feet to order, then estimates weight at about 13 pounds per square foot for every inch of stone thickness (roughly 155 lb per cubic foot), and converts pounds to tons.
Worked example — a 20 ft × 10 ft patio with 1.5 in thick flagstone and 10% waste:
200 sq ft × 1.10 = 220 sq ft → 220 × 1.5 × 13 = 4,290 lb → ÷ 2,000 = 2.15 tons.
200 sq ft × 1.10 = 220 sq ft → 220 × 1.5 × 13 = 4,290 lb → ÷ 2,000 = 2.15 tons.
Why flagstone is sold by the ton
Irregular flagstone varies in thickness and shape, so suppliers sell it by weight. Most yards quote roughly 100–150 square feet per ton at 1–1.5 inches thick, and irregular pieces need 10–15% extra for cutting and fitting.
Frequently asked questions
How many square feet does a ton of flagstone cover?
About 150 square feet at 1 inch thick, 100 square feet at 1.5 inches, and 75 square feet at 2 inches.
How much waste should I allow for a flagstone patio?
Allow 10–15%. Irregular shapes need more cutting and fitting than uniform pavers, so a little extra makes for a better-looking layout.