Drywall Calculator

How the plasterboard (drywall) calculator works

The calculator divides the area to be lined by the area of one sheet, adds waste, and rounds up to whole sheets:

Sheets = round up( area (m²) ÷ sheet area (m²) × (1 + waste % ÷ 100) )

In Australia, plasterboard sheets are commonly 1200 mm wide in lengths from 2400 mm to 6000 mm. A 2400 × 1200 sheet covers 2.88 m².

Worked example: a 4 m × 3.6 m bedroom, walls and ceiling

1. Walls: perimeter 15.2 m × 2.4 m height = 36.48 m²
2. Ceiling: 4 × 3.6 = 14.4 m²
3. Total: 50.88 m²
4. 2400 × 1200 sheets (2.88 m²), waste 10%: 50.88 ÷ 2.88 × 1.10 = 19.4, rounded up to 20 sheets

Using longer sheets reduces joins, which saves setting time and gives a better finish. For the ceiling here, 3600 mm sheets would span the room in one length.

Openings

Don't subtract doors and windows from the wall area. Offcuts from openings rarely get reused cleanly, so the "saving" usually becomes waste. The exception is very large openings like a stacker door. Subtract those.

Picking the board

• Standard 10 mm: most walls
• Ceiling board 10–13 mm: ceilings, where sag resistance matters
• Wet-area board: bathrooms and laundries, installed with the waterproofing system specified
• Fire-rated board: where required between a garage and a house, or between dwellings

Other materials

Allow roughly 1 box of screws per 10–15 sheets, about 0.3 kg of base-coat compound per square metre and around 1.3 m of paper tape per square metre of board. Check the product data for exact figures.

Common mistakes

• Forgetting the ceiling.
• Using 2.4 m sheets on a 2.7 m wall, which leaves a horizontal join at the top.
• Not allowing for wet-area or fire-rated board in the rooms that need it.

How many plasterboard sheets for a 3 × 3 m room?

Walls 12 m × 2.4 m = 28.8 m², plus a 9 m² ceiling = 37.8 m². With 2.88 m² sheets and 10% waste, that is 15 sheets.

Should I hang plasterboard horizontally or vertically?

On walls, horizontal sheets usually mean fewer, lower joins that are easier to finish. Follow the manufacturer's installation guide.

What thickness plasterboard should I use?

10 mm for most walls, 10 or 13 mm ceiling board for ceilings, plus wet-area or fire-rated boards where they are required.

Written by Sam Alex, civil engineer. About the author