How we calculate

Every result on this site comes from a documented formula, not a black box. Here is exactly how the numbers are derived and where our assumptions come from.

Area and volume

Area is length × width in feet (square footage). Volume is length × width × depth, divided by 27 to convert cubic feet to cubic yards. Dimensions entered in inches, centimeters, or meters are normalized to feet before any calculation.

Waste allowances

Materials get cut, trimmed, and occasionally broken, so every quantity includes a waste buffer. Our defaults follow common trade practice — 10% for straight layouts, up to 15–20% for diagonal patterns and large-format pieces — and you can change the percentage on every calculator.

Rounding

You cannot buy a fraction of a tile, board, or post, so counts are always rounded up to the next whole unit. Boxes and bags are rounded up after the waste allowance is applied.

Cost estimates

Cost outputs multiply the quantity by the unit price you enter. Installed price ranges (for example on the deck calculator) apply typical labor multipliers to the material cost and are shown as a low–high range, because local labor rates vary widely.

Accuracy and limits

These tools give reliable planning estimates, not engineered quantities. Always confirm final amounts with your supplier and follow local building codes. If you find an error in a formula, please tell us — corrections are welcome.