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). A pallet is 3,000 to 4,000 lb and comes off a flatbed by forklift. Warning: 1 in stone cracks on a sand bed; dry-laid patios need 1.5 in or thicker, and 1 in stone belongs in mortar over a slab
- Patio area
- 120 sq ft
- 0.83 tons of stone before waste
- Gravel base
- 1.48 cu yd
- 4 in deep, compacted in 2 in lifts. Crusher run compacts 15 to 25%, so order about 20% more than this
- Bedding sand
- 0.37 cu yd
- 1 in of concrete sand or stone dust, screeded and not compacted
- Polymeric sand for joints
- 3 bags
- 50 lb bags, about 50 sq ft per bag with 1 in joints. Joints wider than that need a wide-joint product rated to 4 in, or stone dust
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 and quote coverage per ton for each thickness. Sandstone, bluestone, quartzite and limestone all run 150 to 170 lb per cubic foot, so 1 inch stone covers about 145 square feet per ton and 2 inch about 73; use the yard's own figure if it differs. Flagstone typically runs $300 to $700 per ton in 2026; price tracks distance from the quarry.
Irregular flagstone is fitted like a puzzle and wastes 15 to 20 percent in trimming and rejects; cut dimensional stone wastes closer to 10. Thickness sets the method: 1 inch stone is mortared over a concrete slab and dry-laid patios take 1.5 inch. Irregular pieces over 2 feet across should be 2 inches so they do not snap.
Base, bedding and joints
For a dry-laid patio, excavate the stone thickness plus 5 to 7 inches, compact the soil, and lay geotextile over clay. Place 4 to 6 inches of crusher run or 3/4 minus in 2 inch lifts with a plate compactor; it loses 15 to 25 percent to compaction, so order 20 percent over. Clean #57 or pea gravel never locks up. Screed 1 inch of concrete sand or stone dust, never soft mason sand. Slope 1/4 inch per foot away from the house, tap the stones down with a rubber mallet, and hold the perimeter with edge restraint.
Standard polymeric sand is rated for joints up to about 1 inch; the 1 to 2 inch joints on an irregular patio need a wide-joint product rated to 4 inches or stone dust. Sweep it in dry, blow the surface clean, then mist until the joints refuse water, with no rain for 24 hours. For a mortared patio, set the stone in a 3/4 to 1 inch bed of Type S on a 4 inch slab with control joints; in freeze-thaw regions dry-laid outlasts mortared unless the slab drains.
What this calculator leaves out
The result is stone, base, bedding and joint sand. It leaves out geotextile, edge restraint, the plate compactor (typically $80 to $120 a day in 2026) and delivery at $75 to $150 a load. A 12 by 10 foot patio dug 8 inches deep is 3 cubic yards of spoil to haul.
Mistakes that cost money
- One inch stone on a sand bed cracks the first time a grill is dragged across it; dry-laid patios need 1.5 in or thicker.
- Standard polymeric sand in 1 to 2 in flagstone joints cracks and washes out; wide-joint products are rated to 4 in, or use stone dust.
- Round #57 or pea gravel under the stone never locks up; use crusher run or 3/4 minus, ordered 20% over for compaction.
- A ton of stone in a half-ton pickup: a pallet is 3,000 to 4,000 lb and comes off a flatbed by forklift, so budget delivery.
- Flooding polymeric sand floats the binder onto the stone as a haze; blow the surface clean, mist in passes, no rain for 24 hours.
- Mortaring flagstone onto a gravel base or a cracked slab pops it loose the first winter; mortar needs a sound 4 in slab.
Key facts
- Flagstone weighs about 165 lb per cubic foot, so a ton of 1 in stone covers about 145 sq ft and a ton of 2 in stone about 73.
- A pallet of flagstone weighs 3,000 to 4,000 lb (1.5 to 2 tons), which covers about 145 to 195 sq ft at 1.5 in thick; yards charge a pallet deposit.
- 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
Should I use polymeric sand or regular sand between flagstone?
Polymeric sand if the joints are under about 1 in and the base is compacted and drains; it locks the stones and keeps weeds out. For the 1 to 2 in joints on an irregular patio, use a wide-joint polymeric rated to 4 in or plain stone dust. Stone dust is cheap and easy to top up. Loose regular sand washes out.
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.
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Results are estimates based on standard formulas and typical product specifications. Confirm quantities with your supplier and local code before ordering.