Flagstone Calculator
Calculate how many tons of flagstone you need for a patio or walkway from the area and stone thickness, plus the gravel base, bedding sand and polymeric joint sand.
By CalcBuilt Editorial TeamUpdated September 9, 2026Formulas checked against manufacturer specs, see how we calculate.
Results
- Flagstone to order
- 0.95 tons
- 138 sq ft at 145 sq ft per ton, including 15% waste (1,903 lb)
- Patio area
- 120 sq ft
- 0.83 tons of stone before waste
- Gravel base
- 1.48 cu yd
- 4 in deep, compacted in lifts
- Bedding sand
- 0.37 cu yd
- 1 in of coarse sand or stone dust
- Polymeric sand for joints
- 3 bags
- 50 lb bags, about 50 sq ft per bag with wide joints
Flagstone formula
Area = Length x Width; Order area = Area x (1 + waste %)
Tons = Order area / coverage per ton (1 in = 145, 1.5 in = 97, 2 in = 73 sq ft per ton)
Gravel base (cu yd) = Area x base depth (in) / 12 / 27
Polymeric sand bags = Area / 50, rounded upWorked example
A 15 x 12 ft irregular flagstone patio in 1.5 in stone: 15 x 12 = 180 sq ft. Irregular stone needs 20% waste, so order for 216 sq ft. At 97 sq ft per ton that is 216 / 97 = 2.23 tons.
For a 6 in gravel base: 180 x 0.5 = 90 cubic feet, or 3.33 cubic yards. One inch of bedding sand is 180 / 12 = 15 cubic feet, or 0.56 cubic yards. Joints take 180 / 50 = 3.6, so 4 bags of polymeric sand.
Quick reference
| Patio area | 1 in stone | 1.5 in stone | 2 in stone |
|---|---|---|---|
| 100 sq ft | 0.79 tons | 1.19 tons | 1.58 tons |
| 150 sq ft | 1.19 tons | 1.78 tons | 2.36 tons |
| 200 sq ft | 1.59 tons | 2.37 tons | 3.15 tons |
| 300 sq ft | 2.38 tons | 3.56 tons | 4.73 tons |
| 400 sq ft | 3.17 tons | 4.74 tons | 6.30 tons |
How flagstone is sold
Stone yards sell flagstone by the ton, sometimes by the pallet, and quote coverage in square feet per ton for each thickness. The number depends on the stone: sandstone, bluestone, quartzite and limestone all run about 150 to 170 lb per cubic foot, so 1 inch stone covers roughly 145 square feet per ton and 2 inch stone about 73. Ask the yard for its own coverage figure and use that if it differs.
Irregular flagstone comes in random shapes that must be fitted like a puzzle, which wastes 15 to 20 percent in trimming and rejects. Cut or dimensional flagstone in square and rectangular pieces wastes closer to 10 percent. Buying a little extra also lets you pick the flattest pieces for the walking surface.
Base, bedding and joints
For a dry-laid patio, excavate about 6 to 8 inches, compact the soil, and place 4 to 6 inches of crushed stone in 2 inch lifts, compacting each one. Screed 1 inch of coarse sand or stone dust on top, set the stones with a slight slope of 1/4 inch per foot away from the house, and tap them level with a rubber mallet.
Fill joints with polymeric sand, stone dust or decomposed granite, or plant low groundcover in wide joints. Polymeric sand needs joints at least 1/8 inch wide and hardens when misted, which keeps out weeds and ants. Stone under 1.5 inches thick will crack on a sand base and should be mortared over a concrete slab instead.
Key facts
- Flagstone weighs about 165 lb per cubic foot, so one ton of 1 in stone covers about 145 sq ft and one ton of 2 in stone about 73 sq ft.
- A pallet of flagstone typically weighs 3,000 to 4,000 lb (1.5 to 2 tons) and covers roughly 150 to 250 sq ft depending on thickness.
- Dry-laid flagstone should be at least 1.5 in thick; 1 in stone is for mortared installation over a concrete slab.
- Irregular flagstone wastes 15 to 20% in fitting and trimming; cut rectangular patterns waste about 10%.
- One 50 lb bag of polymeric sand fills about 50 sq ft of 1 in flagstone joints, compared with about 75 sq ft of tight paver joints.
Frequently asked questions
How much area does a ton of flagstone cover?
About 145 sq ft at 1 in thick, 97 sq ft at 1.5 in, and 73 sq ft at 2 in, based on a density of 165 lb per cubic foot. Thicker or denser stone covers less.
How many tons of flagstone for a 12 x 10 patio?
A 120 sq ft patio with 15% waste needs 138 sq ft of stone. In 1 in stone that is 0.95 tons; in 1.5 in stone it is 1.42 tons, and in 2 in stone 1.89 tons.
How thick should flagstone be for a patio?
Use 1.5 to 2 in stone for a dry-laid patio on gravel and sand so pieces do not crack underfoot. Thinner 1 in stone is fine when mortared onto a concrete slab.
What goes under flagstone?
4 to 6 in of compacted crushed stone, then 1 in of coarse sand or stone dust screeded level. A 12 x 10 ft patio needs 1.48 cu yd of gravel at 4 in and 0.37 cu yd of sand at 1 in.
Sources and references
- QUIKRETE Patio Paver Base Sand product page (Quikrete)
- QUIKRETE All-Purpose Gravel product page (Quikrete)
- PolySweep Polymeric Sand product page (SEK Surebond)
Next steps for this project
The usual order for a concrete & masonry project. See all concrete & masonry calculators.
Results are estimates based on standard formulas and typical product specifications. Confirm quantities with your supplier and local code before ordering.