Drywall Calculator — How Many Sheets Do I Need?
Work out how many sheets of drywall (sheetrock / gypsum board) you need for walls and ceilings, including screws and joint compound. Enter your room size in feet or metres, subtract doors and windows, and get a full material list with waste included.
How many sheets of drywall do I need?
Take the wall area, subtract doors and windows, add the ceiling if you are boarding it, and divide by the sheet area — a 4 × 8 ft sheet covers 32 sq ft, a 1200 × 2400 mm sheet 2.88 m². Add 10% for cuts at corners, outlets and ceiling edges, then round up to whole sheets.
What thickness of drywall should I use?
½ in (12.5 mm) is standard for walls and for ceilings on joists at 16 in centres. Step up to ⅝ in (15 mm) for ceilings on 24 in centres, where the thinner board sags between supports, and for fire-rated assemblies — that is Type X, and it is specified, not optional.
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How the drywall sheet count is calculated
- 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 (a 4×8 ft sheet ≈ 1.2 × 2.4 m = 2.88 m²)
- 5Apply 10% waste for cuts at corners, outlets and ceiling edges
- 6Round up to the nearest whole sheet
Worked example
Room: 4 × 3 m (≈ 13 × 10 ft), walls 2.4 m (8 ft) 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 4×8 ft (1.2×2.4 m) drywall.
Frequently asked questions
How many sheets of drywall do I need for a 12×12 room?
A 12×12 ft room with 8 ft ceilings has approximately 36 m² (384 sq ft) of wall area. With 10% waste you need about 14 sheets of standard 4×8 ft drywall — more if you also board the ceiling.
What thickness drywall should I use?
1/2 inch (12.5 mm) is standard for walls and ceilings. Use 5/8 inch (15 mm) for fire-rated assemblies or extra acoustic performance. 3/8 inch is only for low-traffic areas or curved walls.
How many screws per sheet of drywall?
Along sheet edges: about 200 mm (8 in) centres; on intermediate studs: about 300 mm (12 in) centres. That works out to roughly 30–36 screws per 4×8 ft sheet — the calculator counts them for you.
How much joint compound do I need per sheet?
Allow approximately 0.5–0.7 kg (1–1½ lb) per sheet for a standard 3-coat taping job. A 20 kg (44 lb) bucket covers roughly 30–40 sheets.
Should I hang drywall horizontally or vertically?
Horizontal installation creates fewer butt joints and is generally preferred for walls. Vertical installation simplifies cutting in rooms with standard ceiling heights.
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