Drywall Calculator
Drywall (plasterboard / gypsum board) is sold in large sheets, and every offcut smaller than half a sheet is usually waste. This calculator converts your wall and ceiling area into sheet counts, screws and joint compound.
Get the total area from the Wall Area Calculator (add the ceiling if you are covering it), then choose your sheet size.
Enter valid values to see the results.
Formula
Sheet areas: 2.5 × 1.2 m = 3 m² (4 × 8 ft = 32 ft²); 3.0 × 1.2 m = 3.6 m² (4 × 12 ft = 48 ft²). Screws: ~30 per sheet (every 30 cm on studs). Joint compound: ~0.35 kg/m² (0.032 lb/ft²) for tape and two finish coats.
How to measure
- Measure each wall width × height and the ceiling length × width; add everything together.
- Do not deduct standard doors and windows — offcuts around them become waste anyway; deduct only full-height openings wider than a sheet.
- Plan the layout: horizontal sheets on walls reduce butt joints; ceilings always run perpendicular to joists.
Worked example
Practical tips
- Use 12.5 mm (½ in) board for walls and ceilings; 9.5 mm only for curved surfaces.
- Stagger vertical joints between rows like brickwork — aligned joints crack.
- Larger 12 ft sheets mean fewer joints but need two people and clear access to the room.
- Buy moisture-resistant (green) board for bathrooms and kitchens.
Waste allowance
Use 10% waste for typical rooms and up to 15% for rooms with many openings, angles or soffits. Offcuts under half a sheet rarely find a use.
Sheet coverage comparison
| Sheet size | Area | Sheets per 100 m² |
|---|---|---|
| 2.5 × 1.2 m (4×8 ft) | 3.0 m² / 32 ft² | 34 |
| 3.0 × 1.2 m (4×12 ft) | 3.6 m² / 48 ft² | 28 |
Common mistakes
- 1 Forgetting the ceiling when counting area — it often adds 20–30% to the total.
- 2 Deducting every window: the cut-out pieces are waste, so the sheet count barely changes.
- 3 Choosing 12 ft sheets for a small room with narrow doors — they may not physically fit inside.
- 4 Under-ordering screws: 30 per sheet is the minimum for 40 cm stud spacing.
Frequently asked questions
How many drywall sheets for a 12×12 ft room?
Walls plus ceiling at 8 ft height ≈ 528 ft². With 10% waste and 4×8 sheets: 581 ÷ 32 ≈ 19 sheets; with 4×12 sheets: 13.
How many screws per sheet of drywall?
About 30 screws per 4×8 sheet on walls (studs every 16 in) and up to 40 on ceilings. Buy 1 kg (≈ 250 pcs) per 8 sheets.
How much joint compound do I need?
Roughly 0.35 kg per m² (a 25 kg bucket per 70 m²) for taping and two finish coats. Textured finishes need more.
Should sheets hang vertically or horizontally?
Horizontally on walls: it reduces the length of butt joints and puts the long tapered edge at a comfortable working height. Ceilings always perpendicular to joists.
Can I use offcuts?
Yes — pieces wider than 30 cm work above doors and windows. Plan the layout so offcuts land in these zones before ordering extra sheets.