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Flagstone Patio Calculator

Enter your patio area and stone thickness to estimate flagstone tonnage.

How it is calculated

The tool starts from a rule of thumb: one ton of flagstone covers 120 square feet at a thickness of 1.5 inches. Coverage scales inversely with thickness: coverage per ton = 120 × (1.5 / thickness) sq ft, with thickness in inches. Then tons = area / coverage per ton, with the patio area in square feet. If thickness is left blank it uses 1.5 inches, and area and thickness must be above zero. The result is the weight of stone for the stated area only: it contains no allowance for breakage, cutting waste, irregular gaps or an uneven surface. Actual stone density and coverage vary by type and supplier, so confirm with the yard before ordering.

Worked example

A patio of 240 sq ft laid with 2 in. stone. Coverage per ton: 120 × (1.5 / 2) = 120 × 0.75 = 90 sq ft. Tons: 240 / 90 = 2.67 tons. The same area in 1.5 in. stone would need 240 / 120 = 2.00 tons, so the extra half inch of thickness adds about a third more weight.

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Common mistakes

  • Entering the area in square metres or the thickness in centimetres. The tool is built on square feet and inches; 3 cm is about 1.2 in, not 3.
  • Treating the tonnage as the final order. Flagstone is cut and trimmed, and some pieces break, so suppliers typically advise ordering extra; the tool gives the net figure only.
  • Using the thickness of the sand or gravel base. Only the stone's own thickness belongs in the field; the base layer is bought separately.
  • Assuming 1.5 inches when the supplier sells thicker stone. Leaving the field blank applies 1.5 in., and a 2 in. stone needs a third more tonnage for the same area.
  • Measuring a rectangular footprint for a curved patio. Enter the real paved area after subtracting any planting beds or steps.

About this calculator

Flagstone — flat, irregular slabs of sedimentary rock like sandstone, limestone or quartzite — is sold by weight rather than by piece because its thickness and shape vary, so ordering the right amount means converting a patio's square footage into tons rather than counting stones. A common industry rule of thumb is that one ton covers roughly 120 square feet at 1.5 inches thick, with coverage scaling down as the chosen thickness increases (a thicker stone naturally covers less area per ton).

Patio area and stone thickness are converted into tons of flagstone, the same conversion landscapers and stone yards use to quote patios, walkways and dry-stack walls, so you avoid paying for a surplus load or running short halfway through.

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Comments (1)

  • Editorial team

    Stone yards often quote a few thicknesses, so run each one before you compare prices. For a 240 sq ft patio the tool shows 2.00 tons at 1.5 in. but 4.00 tons at 3 in., because coverage per ton halves as thickness doubles. A thicker stone can look cheaper per ton yet cost far more overall. The figure is net, so ask the yard what spare to add. What thickness did your supplier recommend for your base?

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