Flagstone Calculator

1. Enter the area to cover in square feet.
2. Pick the flagstone thickness, or enter a supplier coverage.
3. Add a waste allowance.
4. Set a gravel base depth, then read the flagstone tons and the base.

Here is what each result line means:

For the compacted base in depth and volume, see the gravel base calculator, or for a mortar bed over a slab the concrete slab calculator.

A flagstone calculator estimates how much flat paving stone you need for a patio, walkway or terrace. Flagstone is sold by weight, in tons, but you lay it by area, so the tool converts the area you want to cover into tons using a coverage figure.

Coverage is the square feet one ton will lay, and it falls as the stone gets thicker, because a ton of thick stone is fewer square feet. The tool also sizes the gravel base that a stable flagstone surface needs underneath.

The area, grossed up for waste, is divided by the coverage per ton to get the tons. The base is the area times the base depth, converted to cubic yards and then to tons of gravel.

1. Gross the area up by the waste allowance.
2. Divide by the coverage for the thickness to get the tons.
3. Multiply the area by the base depth for the base volume.
4. Convert the base to cubic yards and tons of gravel.

Supplier charts give roughly 130 to 150 square feet per ton at 1 inch, 90 to 100 at 1-1/4 inch and 70 to 80 at 2 inches. The figures vary with joint spacing, so your supplier number wins.

Suppose you are paving a 200 square foot patio in 1-1/2 inch flagstone at about 85 square feet per ton, with 10 percent waste and a 4 inch base.

Calculation: the area with waste is 200 times 1.10, or 220 square feet. Divided by 85 that is about 2.6 tons of flagstone. The base is 200 times 4 inches, about 67 cubic feet, roughly 2.5 cubic yards, or about 3.5 tons of gravel.

The lesson: thickness sets the coverage, and the base can out-weigh the stone itself.

Thickness

Thicker stone weighs more per square foot, so a ton covers less. Going from 1 inch to 2 inch stone nearly doubles the tons for the same area.

Joint Spacing

Wide gaps between stones stretch the coverage; tight joints use more stone. Supplier figures assume a typical joint.

Stone Shape and Grade

Irregular, broken flagstone wastes more in fitting than square-cut pieces, so it needs a bigger waste allowance.

Base Depth

A deeper base on soft or frost-prone ground adds a lot of gravel tonnage, often more than the stone.

Flat stone products are sized in different ways.

For uniform units, use the concrete paver calculator. To cost a comparable stamped surface, see the stamped concrete cost calculator.

Patios and Terraces

Turn a patio area into tons to order and a base to prepare.

Walkways and Paths

Size a garden path, allowing for cutting curves and edges.

Stepping Stones

Estimate loose flagstone set as steppers across a lawn.

Budgeting

Get the tonnage to price the stone and the base before you buy.

1. Using One Coverage for Every Thickness

Coverage halves from 1 inch to 2 inch stone. Match the figure to the thickness you are buying.

2. Forgetting the Base

Flagstone needs a compacted gravel base. The base gravel often weighs more than the stone, so do not leave it out of the order.

3. Skipping Waste

Irregular stone wastes a lot in cutting and fitting. Add 10 to 15 percent, more for busy shapes.

4. Ignoring Joint Width

Tight joints use more stone than the chart assumes. Plan the joint and adjust the coverage.

5. Trusting a Generic Chart

Coverage varies by quarry and grade. Get the supplier figure for the exact stone before ordering.

The math is exact for the inputs, but coverage is a supplier estimate that shifts with joint spacing and stone shape, so treat the tonnage as a planning figure and confirm the coverage before you order.

About 130 to 150 square feet at 1 inch thick, 90 to 100 at 1-1/4 inch and 70 to 80 at 2 inches, by supplier charts. Coverage depends on the joint spacing.

About 2.4 tons at 1-1/2 inch thick with 10 percent waste. Thinner stone needs less and thicker stone more. Confirm the coverage with your supplier.

Flagstone is sold by weight. A ton of thick stone is fewer square feet than a ton of thin stone, so thicker stone covers less area per ton.

Typically 1 to 2 inches. Thinner stone (1 to 1-1/4 inch) suits a mortar bed or tight joints; 1-1/2 to 2 inch stone is common for a sand-set patio.

Yes. A compacted gravel base, often about 4 inches, with a sand or stone-dust setting bed, keeps the stone stable and draining. Deeper on soft or frost-prone ground.

About 10 to 15 percent for cutting and fitting. Irregular, broken flagstone wastes more than square-cut pieces, so use the higher end.

Roughly 13 to 15 pounds per square foot at 1 inch thick, scaling with thickness, depending on the stone type. A ton is about 2,000 pounds of stone.

Both work. Sand-set over gravel is common for patios and paths; a mortar bed over a concrete slab is used where a rigid, permanent surface is wanted.

Divide the area, with waste added, by the coverage per ton for your stone thickness. This tool does it for you once you enter the area and thickness.

No. The calculation runs entirely in your browser and nothing you enter is stored or sent anywhere.

• Select Stone: Frontier Sandstone Product Guide (coverage charts) (flagstone coverage per ton by thickness).
• Hunker: How to Estimate Flagstone (area-to-tonnage method and waste).
• BIA Technical Note 10, Dimensioning and Estimating Brick Masonry (Brick Industry Association; masonry area estimating).