Drywall Calculator
Works out plasterboard sheets for a room, with the screws, tape and joint compound. Covers both a tape-and-joint finish and a skim-plaster one, which use very different amounts of compound.
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The formula
area = perimeter × height − openings (+ length × width for the ceiling) sheets = ceiling(area × (1 + waste) ÷ sheet area) screws ≈ 12/m² walls, 16/m² ceiling; compound ≈ 0.7 kg/m² taped
Sheets round up hard on a small room because they are large units — a 2.88 m² sheet left two-thirds unused is still a whole sheet bought. The consumables scale with area more smoothly, which is why they are given per square metre.
What to watch out for
Decisions that change the order:
- Sheet size. Longer sheets mean fewer joints to fill, but 2700 and 3000 mm boards are heavy and awkward through a doorway. 2400 is standard for a reason.
- Board thickness follows the stud spacing: 12.5 mm at 400 mm centres, 15 mm at 600. Ceilings at 600 mm centres want 15 mm or they sag between joists.
- Finish. Tape-and-joint uses about 0.7 kg of compound per square metre over three coats. A skim finish uses compound only at the joints and then a plaster skim over everything, which is a different trade.
Frequently Asked Questions
How many sheets of drywall do I need?
Work out the wall area (perimeter × height, less openings) plus the ceiling, add 10% waste and divide by the sheet area. A 4 × 3.5 m room with 2.4 m walls, one door, two windows and a ceiling is about 47 m², which is 18 standard sheets.
How many screws per sheet of drywall?
About 32–36 for a 1200 × 2400 sheet on a wall at 300 mm centres, and 45 or so on a ceiling at 230 mm. Per square metre that is roughly 12 on walls and 16 overhead.
How much joint compound per square metre?
About 0.7 kg for a full tape-and-joint finish across three coats, so a 20 kg bucket does roughly 28 m². If the board is being skim plastered, compound goes only on the joints and 0.25 kg/m² is enough.