Drywall is cheap per sheet and miserable to run short of, because a missing sheet stops the whole room. This calculator measures the walls (and ceiling, if you want it), subtracts doors and windows, and divides by your sheet size — then estimates the screws, tape and joint compound that finish the job.
The formula
Wall area is the room's perimeter times its height: 2 × (length + width) × height. Standard openings subtract about 21 ft² per door and 15 ft² per window (1.95 m² / 1.4 m²) — the offcuts from those openings get reused around them, which is part of why the waste allowance can stay at 10% for plain rooms.
Choosing a sheet size
4 × 8 ft sheets are easiest to carry and fit through doors, but longer sheets (4 × 10, 4 × 12 ft) mean fewer seams to tape on long walls and ceilings — pros pick the longest sheet that reaches the ceiling height in one piece or spans the wall cleanly. In metric countries, 1200 × 2400 mm is the workhorse. Whatever you choose, ½ in board is standard for walls; ceilings on 24 in joist spacing and garage walls often call for ⅝ in or sag-resistant board.
The finishing estimates
Screws run about 32 per sheet (field screws every 12–16 in on walls, tighter on ceilings). Joint tape works out near 0.37 ft per ft² of installed board including butt joints and corners. Ready-mix compound goes about one 5-gallon bucket per 450 ft² across three coats. Treat all three as shopping estimates — technique and finish level move them — and buy from somewhere that takes returns.
Worked example
A 12 ft × 10 ft room with 8 ft ceilings, walls only, one door and one window: wall area = 352 ft², minus 36 ft² of openings = 316 ft². With 4 × 8 ft sheets (32 ft²) that is 9.9 sheets exact — 11 sheets with a 10% allowance, about 352 screws, 1 roll of tape and 1 bucket of compound.
How to use this tool
- Measure the room and choose units and sheet size.
- Pick walls only, or walls plus ceiling.
- Subtract the doors and windows; leave closets you plan to board.
- Keep a 10% allowance for cuts and the sheet that always gets damaged.
- Use the screw, tape and mud lines as your finishing shopping list — and keep receipts for returns.
Hanging order matters
Ceilings go up first, then walls from the top down, so wall boards support the ceiling edges. Stagger butt joints so no two end in line, and keep factory edges together at seams wherever possible — tapered edges hide tape; cut edges telegraph it.