Total wall/ceiling area (ft²), sheet area (default 4×8 = 32 ft²), waste %—sheets to buy (rounded up).
With wall area (ft²), nominal sheet coverage (ft² per sheet), and a waste/add‑on percent 0–200, the model computes need = area × (1 + waste÷100) ÷ coverage and reports ⌈need⌉ whole sheets. The second line shows the unrounded “sheet‑equivalents” for reference.
This calculator uses plain decimal numbers. If a result looks wrong, check whether you used a comma instead of a dot (or vice versa) where the field expects one.