Drywall calculator

How the sheets are counted

Drywall is counted by area: the board to hang, plus a waste allowance, divided by the area of one sheet and rounded up to whole sheets. That is how Georgia-Pacific’s calculator and Lowe’s buying guide do it, and unlike wallpaper or carpet it is honest — an offcut from one wall really does fill a gap on the next.

A 12 × 12 ft room with 8 ft walls, allowing 10% for waste:

Longer sheets buy the same board in fewer pieces, and fewer pieces means fewer joints to tape.

Doors and windows are figured solid

Nothing is taken off for doors and windows unless you ask. The CGC Gypsum Construction Handbook says professional estimators frequently count walls with no openings at all: the board goes on over the opening and the piece cut out of it is part of the waste. CertainTeed’s calculator says the same thing directly — do not subtract doors, windows or outlets.

The handbook names the exceptions: large picture windows and large door openings. For those, tick take doors and windows off the walls and enter them under each room. They are the same doors and windows the paint and baseboard pages use, so anything already entered there is already here.

Which sheet

US drywall comes 4 ft or 54 in wide and 8 to 16 ft long; USG lists both widths for its ½ in UltraLight panels. Two rows of 54 in sheets hung sideways make exactly 9 ft, which two rows of 4 ft sheets cannot. On 9 ft walls in the same 12 × 12 ft room, 432 sq ft of wall takes 10 sheets of 4 × 12 ft or 9 of 54 in × 12 ft.

British plasterboard is 1200 mm wide, or 900 mm for the smaller boards. British Gypsum’s 12.5 mm wallboard comes in 900 × 1800, 900 × 2400 and 1200 × 2400, 2500, 2700 and 3000 mm, with 2300 and 3600 mm lengths in the tapered-edge board only — so a board hung upright can reach from floor to ceiling in most rooms. A 3.6 × 3.6 m room with 2.4 m walls has 34.56 m² of wall and takes 14 boards of 1200 × 2400 mm.

How much waste

Georgia-Pacific’s calculator adds 10% for cut-outs and waste, and Lowe’s says to add 10% after dividing by the sheet. National Gypsum’s and CertainTeed’s calculators add nothing. The 10% here is editable: a plain box of a room wastes less than one full of corners, soffits and openings.

Tape, compound and screws

The rest of the shopping list comes from USG’s published rates, per 1,000 sq ft of board hung: about 370 ft of paper joint tape, and about 10 gallons of all-purpose joint compound. Screws follow the CGC handbook’s table for 4 × 8 board on framing 16 in apart: 875 per 1,000 sq ft screwed every 16 in, as USG spaces them on walls, and 1,094 screwed every 12 in, as it spaces them on ceilings. The handbook says to allow extra for loss.

For the walls and ceiling of the 12 × 12 ft room that is about 195 ft of tape — one 250 ft roll — 5.3 gallons of compound, two 4.5 gallon pails, and 494 screws.

These are USG’s figures in US units, converted for a metric page rather than replaced. USG’s own metric figure for compound, 37.8 litres per 100 m², is not the conversion of its 10 gallons per 1,000 sq ft, which comes to 40.7 litres — so the page converts the US figure and says so.

What this version does not do yet

• Sheet layout: which way to hang each sheet and where the joints fall.
• Corner bead, trims and insulation, and the choice between regular, moisture- and fire-resistant board.
• Finish levels: a smooth Level 5 finish takes more compound than the rates above.