Flagstone is sold by the ton or by the pallet, not by the square foot, so the question is how many square feet a ton will cover. That depends on two things: how thick the stones are and how dense the rock is. Thin 1 inch stone covers about twice as much ground per ton as 2 inch stone. This flagstone calculator turns your patio size, stone thickness and density into tons, allowing for joints between stones and waste from fitting, then adds the gravel base and sand bedding. A 12 × 14 ft patio of 1.5 inch flagstone takes about 1.6 tons, roughly 108 ft² per ton.
Prefer uniform concrete pavers? Use the paver calculator. To fill the joints, see the polymeric sand calculator.
How to use the flagstone calculator
- Enter the patio or path length and width. For curved shapes, use the area of the bounding rectangle and raise waste.
- Enter the average stone thickness. Patio flagstone is commonly 1 to 2 inches; thinner stone should be set on a mortar bed over concrete.
- Enter the stone density if your supplier gives one; 150 lb/ft³ is a reasonable middle value.
- Set the share of the area taken by joints (tighter fit means more stone) and a waste allowance for cutting and fitting irregular pieces.
- Enter base and bedding depths for a dry-laid patio: commonly 4 inches of compacted gravel and 1 inch of sand or stone dust.
Formula
Base gravel tons use 1.4 tons/yd³ and sand 1.35 tons/yd³.
Worked example
A 14 × 12 ft patio of 1.5 inch flagstone at 150 lb/ft³, with 10% joints, 10% waste, 4 inches of gravel base and 1 inch of sand.
- Area: 14 × 12 = 168 ft². Stone area: 168 × 0.90 = 151.2 ft².
- Stone volume: 151.2 × 1.5 ÷ 12 = 18.9 ft³ × 150 = 2,835 lb × 1.10 = 3,119 lb = 1.56 tons.
- Coverage: 168 ÷ 1.56 = about 108 ft² per ton.
- Base: 168 × 4 ÷ 12 = 56 ft³ × 1.10 = 2.28 yd³ (about 3.2 tons). Sand: 168 × 1 ÷ 12 × 1.10 = 0.57 yd³ (about 0.77 tons).
Square feet of flagstone per ton
Patio area covered by one ton at each thickness and density, with 10% of the area in joints and no waste.
| Stone thickness | 140 lb/ft³ | 150 lb/ft³ | 165 lb/ft³ |
|---|---|---|---|
| 1 in | 190 ft² | 178 ft² | 162 ft² |
| 1.5 in | 127 ft² | 119 ft² | 108 ft² |
| 2 in | 95 ft² | 89 ft² | 81 ft² |
| 2.5 in | 76 ft² | 71 ft² | 65 ft² |
So 1.5 inch stone at 150 lb/ft³ covers about 119 ft² per ton before waste. Suppliers' rules of thumb usually fall in the same range; ask yours, because thickness varies within every pallet.
Dry-laid vs mortared flagstone
A dry-laid patio sits on compacted gravel and a sand or stone-dust setting bed, with joints filled with sand, polymeric sand, gravel or plants. It drains well and tolerates frost if the base is deep enough. Mortared flagstone is set on a concrete slab and is better for thin or very irregular stone. The Interlocking Concrete Pavement Institute's guidance on base thickness and compaction for pavers is a useful reference for dry-laid stone, too. Order base and bedding with the gravel calculator and sand calculator; for decorative edging, see the landscape rock calculator.
Caveats and assumptions
- Flagstone thickness varies within a pallet; use the supplier's average.
- Density depends on the rock type. Ask the yard for the weight per pallet and the square feet it covers when possible.
- Steps, walls and coping use thicker stone and more waste; calculate them separately.
- Base depth depends on soil and frost conditions; clay or freezing climates often need deeper bases.
Frequently asked questions
How much flagstone do I need per square foot?
At 1.5 inches thick and 150 lb/ft³ with 10% joints, about 17 lb of stone per ft² of patio, before waste.
How many square feet does a ton of flagstone cover?
Roughly 160 to 190 ft² for 1 inch stone, 110 to 125 ft² for 1.5 inch, and 80 to 95 ft² for 2 inch, depending on rock density, allowing about 10% joints and no waste.
How much flagstone for a 12x12 patio?
A 144 ft² patio of 1.5 inch flagstone needs about 1.35 tons with 10% joints and 10% waste.
How thick should flagstone be for a patio?
For dry-laid patios, about 1.5 to 2 inches is common so stones don't crack. Thinner stone is usually mortared onto a concrete slab.
What goes under flagstone?
For a dry-laid patio, typically 4 inches or more of compacted gravel base and about 1 inch of sand or stone dust to bed the stones.
Sources
- Natural Stone Institute — consumer resources — stone types and selection
- Interlocking Concrete Pavement Institute — base, bedding and compaction practice for segmental paving
- NIST — Unit Conversion — cubic feet, cubic yards and tons
This calculator gives estimates for planning and education. Check measurements, local codes, supplier specs and your school's official policy before relying on a result. See our disclaimer and how we build and check calculators.