How to calculate square footage for stone
Square footage for stone is the flat area of the bed you're covering, measured in square feet — length times width. That number is where every stone project starts, but for loose decorative rock it's only half the answer. Because stone is poured to a depth rather than laid flat like tile, suppliers sell it by volume (cubic yards) or weight (tons), so you have to convert your area into one of those units before you can place an order.
Start by measuring each bed as a rectangle. For a curved or L-shaped area, break it into simple rectangles, calculate the square footage of each, and add them up — the same approach works for a border that wraps around a patio. Once you have the total area, the calculator above converts it to cubic yards for whatever depth you pick, so you're not guessing at a delivery quantity.
Turning square feet into cubic yards and tons
The conversion is straightforward: area in square feet, times depth in feet, divided by 27 (the number of cubic feet in a cubic yard). A quick rule of thumb is that one cubic yard of stone covers about 100 square feet at 3 inches deep — roughly 160 square feet at 2 inches for a light top-up, or about 80 square feet at 4 inches for a deeper, weed-suppressing layer. Choose your depth first, because it changes the order more than anything else.
Many yards sell by the ton, so it helps to know that a cubic yard of stone weighs about 1.3–1.5 tons depending on the rock. If you're also pricing a gravel base or comparing materials, the depth-to-volume math is identical. Once you have your cubic yards or tons, drop the figure into the cost calculator with your price per unit to turn the measurement into a delivered budget.
Loose stone vs. flagstone — two different measurements
Not all stone is ordered the same way. Loose material — river rock, pea gravel, crushed stone, lava rock — is bought by the cubic yard or ton because it fills a depth. Flagstone, on the other hand, is a flat paving stone sold by the square foot, so your measured area is the order quantity almost directly; just add about 10% for cutting and fitting irregular pieces.
Knowing which type you're buying keeps you from over- or under-ordering. If you're covering a bed or a dry creek, think in cubic yards and depth. If you're laying a patio walking surface, think in square feet and let the area drive the order. When in doubt, ask the supplier how they price the specific stone you want, since the same rock can sometimes be sold either way.