Plasterboard & Drywall Calculator — Sheets, Screws & Jointing
Calculate how many plasterboard or drywall sheets you need for any room, including waste. Supports standard and custom sheet sizes, and accounts for windows, doors and ceiling areas.
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Plan the whole job — not just this calculation
Save results to a project: budget and shopping list build themselves, and the whole plan exports as a PDF. Draw your floor plan and room sizes pre-fill the calculators.
How the drywall calculator works
- 1Calculate total wall area: perimeter × wall height
- 2Subtract opening area: doors and windows (width × height each)
- 3Add ceiling area if selected (room length × width)
- 4Divide net area by sheet area (e.g. 1.2 × 2.4 m = 2.88 m²)
- 5Apply 10% waste for cuts at corners, outlets and ceiling edges
- 6Round up to nearest whole sheet
Worked example
Room: 4 × 3 m, walls 2.4 m high. One door (0.9×2.1 m), one window (1.2×1.2 m). Ceiling included.
Wall area: 33.6 m² − 3.33 m² openings = 30.27 m². Ceiling: 12 m². Total: 42.27 m² + 10% = 46.5 m². You need 17 sheets of 1.2×2.4 m drywall.
Frequently asked questions
How many drywall sheets do I need for a 12×12 room?
A 12×12 ft (3.66×3.66 m) room with 8 ft (2.44 m) ceilings has approximately 36 m² of wall area. With 10% waste you need about 14 sheets of standard 1.2×2.4 m drywall.
What thickness drywall should I use?
12.5 mm (1/2 inch) is standard for walls and ceilings. Use 15 mm (5/8 inch) for fire-rated assemblies or for extra acoustic performance. 9.5 mm is only for low-traffic areas or curved walls.
How far apart should drywall screws be?
Along sheet edges: 200 mm centres. On intermediate studs (field): 300 mm centres. Screws must be at least 12 mm from sheet edges to avoid breaking the paper face.
Should I hang drywall horizontally or vertically?
Horizontal installation creates fewer butt joints (the ends without a tapered edge) and is generally preferred for walls. Vertical installation simplifies cutting in rooms with standard ceiling heights.
How much joint compound do I need per sheet of drywall?
Allow approximately 0.5–0.7 kg of joint compound per sheet for a standard 3-coat taping job. A 20 kg bucket covers roughly 30–40 sheets.