Flagstone Calculator
A flagstone calculator divides patio area by about 110 sq ft per ton for 1.5 to 2 in stone. A 15 × 12 ft patio (180 sq ft) needs 1.64 tons, 1.80 with 10% waste.
How much flagstone do I need?
A flagstone calculator turns the area of a patio or path into the tons of stone to order. Tons = area in square feet ÷ 110, where 110 square feet per ton is a typical coverage for flagstone 1.5 to 2 inches thick. A 15 × 12 ft patio covers 180 square feet and needs 1.64 tons, or 1.80 tons with the 10% waste box ticked. At $450 per ton that is $736.36, or $810.00 with waste.
The price field is a placeholder. Flagstone prices vary a lot by stone type, color, and distance from the quarry, so enter your stone yard’s per-ton price.
The formula in plain words
- Area = length × width, in square feet.
- Tons = area ÷ 110.
- With waste = tons × 1.10.
- Cost = tons × price per ton.
Joints are included in the area. A patio with wide, planted joints uses a little less stone than one with tight joints, which works in your favor.
Worked examples
Back patio: 15 × 12 ft, $450/ton
- Area: 15 × 12 = 180 sq ft
- Tons: 180 ÷ 110 = 1.64 tons, $736.36
- With 10%: 1.80 tons, $810.00
Garden walkway: 30 ft long × 3 ft wide, $450/ton
- Area: 30 × 3 = 90 sq ft
- Tons: 90 ÷ 110 = 0.82 tons, $368.18
- With 10%: 0.90 tons, $405.00
Most yards sell partial pallets, but some have a minimum. Ask before you plan a sub-ton order.
Flagstone needed by patio size (110 sq ft per ton)
| Area | Net tons | Tons with 10% |
|---|---|---|
| 45 sq ft (stepping path) | 0.41 | 0.45 |
| 144 sq ft (12 × 12 ft) | 1.31 | 1.44 |
| 200 sq ft | 1.82 | 2.00 |
| 300 sq ft | 2.73 | 3.00 |
| 400 sq ft | 3.64 | 4.00 |
| 720 sq ft (30 × 24 ft) | 6.55 | 7.20 |
Rough coverage by thickness
| Flagstone thickness | Approx. sq ft per ton | Typical use |
|---|---|---|
| About 1 in or less | 150 to 200 | Mortar-set on concrete, wall veneer |
| 1.5 to 2 in | 100 to 120 (calculator: 110) | Dry-laid patios and paths |
| 2 to 3 in | 70 to 90 | Stepping stones in lawn, heavy-use areas |
These are rough ranges often used by stone yards. If your stone is thinner or thicker than 1.5 to 2 inches, divide your area by the supplier’s figure instead of using the calculator’s result.
What goes under flagstone
A dry-laid patio usually has three layers:
- Compacted base: about 4 in of crushed stone with fines. Size it with the paver base calculator.
- Setting bed: about 1 in of coarse sand or stone screenings. The paver sand calculator gives the volume.
- Joint fill: sand, fine gravel, polymeric sand, or soil for moss and creeping thyme. For polymeric sand, use the polymeric sand calculator as a starting point; wide flagstone joints use more than paver joints.
Choosing pieces at the stone yard
Flagstone is often sold by the pallet, and the pieces on one pallet can range from dinner-plate size to slabs two people struggle to lift. Larger flags make a patio look calmer and leave fewer joints, but they are heavy and harder to level. Mixing a few large anchor stones with mid-size pieces is a common approach. If you can, pick the pallet yourself and check the thickness of several stones with a tape.
How to measure
- Measure the full finished footprint, edge to edge, in feet.
- Split curved or free-form patios into rectangles, or measure the longest length and average width.
- For a stepping-stone path, measure only the area covered by stones, not the whole strip of lawn.
Common mistakes
- Assuming one coverage for every thickness. Thick stone covers far less per ton.
- Skipping the base. Flagstone set straight on soil rocks and sinks.
- Ordering the net amount. Irregular stone always needs spare pieces to choose from.
- Mixing lots. Stone color varies between quarry runs. Order everything at once.
For uniform concrete pavers instead of natural stone, the paver calculator counts pieces.
Frequently asked questions
How much area does a ton of flagstone cover?
This calculator uses 110 sq ft per ton, a common figure for stone about 1.5 to 2 inches thick. Thin stone of 1 inch or less covers noticeably more per ton, and thick 2 to 3 inch slabs cover less. Your quarry or stone yard can give the coverage for the exact product.
Why is flagstone sold by the ton instead of by the piece?
Each flag is a different shape and size, so counting pieces is meaningless. Yards weigh pallets or loader buckets instead. That is why the calculator converts area to tons.
Do I need a mortar bed, or can flagstone go on sand?
Both work. Dry-laid flagstone sits on a compacted gravel base with a sand or fine screenings bed and suits casual patios and paths. Mortar-set flagstone goes on a concrete slab and gives a tighter, more formal look. Dry-laid is the common DIY method.
How much waste should I add for flagstone?
Start with the 10% box. Irregular stone needs trimming, and some pieces will not fit anywhere. Large patios with tight joints, or stone that breaks easily, may need 15%. The 180 sq ft default goes from 1.64 to 1.80 tons with 10% added.
Does stone type change the coverage?
Thickness matters most, but density varies too. Bluestone, sandstone, limestone, and quartzite all weigh slightly different amounts per cubic foot. For a large order, use the supplier's coverage figure for that stone.
Estimates only. Verify quantities with your supplier before purchasing.