How this calculator works
The wall area is twice the length plus width times the height; ticking the ceiling adds the floor-sized rectangle on top. That area, increased by the waste allowance, is divided by the sheet area and rounded up. Tape, compound and screws follow from trade ratios: about 40 ft of tape per 4 by 8 sheet, 0.01 gallons of compound per square foot of board and roughly one screw per square foot. These are planning figures, not a purchase list carved in stone.
Formula
A = 2 × (L + W) × H + ceiling area; sheets = ceil(A × (1 + waste%) ÷ sheet area); tape ≈ 40 ft per sheet; compound ≈ 0.01 US gal/ft² of board; screws ≈ 1 per ft². One US gallon is 3.785 L.
Worked example
A 12 × 10 ft room with an 8 ft ceiling: walls 352 ft² plus ceiling 120 ft² is 472 ft². With 15% waste and 4 by 8 ft sheets that is 17 sheets, 680 ft of tape and 5.4 gallons of compound.
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Frequently asked questions
Why 15% waste for drywall?
Boards arrive in fixed sizes, so every room leaves an offcut, and door and window cut-outs cannot be reused elsewhere. Fifteen percent is the usual allowance for a room; a plain rectangle can use 10%.
Does 1/2 in board or 5/8 in board change the count?
No for area. The sheet count depends on the dimensions of the board, not its thickness. Thicker fire-rated board for ceilings in Canada follows the same sheet sizes but is heavier to hang.
Is the ceiling always boarded?
Only if the existing ceiling is being replaced or finished. Untick the ceiling for a basement where the ceiling is left exposed or covered by a suspended grid.