Drywall formula
Wall area = 2 × (Length + Width) × Height − Openings
Sheets = (Wall area + Ceiling area) × (1 + Waste) ÷ Sheet area
Sheets = (Wall area + Ceiling area) × (1 + Waste) ÷ Sheet area
Example: A 12 × 12 ft room with 8-ft walls has 384 sq ft of wall. Subtracting one door (21 sq ft) and two windows (30 sq ft) leaves 333 sq ft; adding the 144 sq ft ceiling gives 477 sq ft. With 10% waste, that is 17 sheets of 4×8 drywall and about 544 screws.
Tips
- Hang ceiling sheets first, then walls from the top down.
- Use moisture-resistant board in bathrooms and cement board behind tile.
- Stagger seams and avoid joints at the corners of doors and windows.
Covering the walls afterwards? Try the wallpaper calculator.
Frequently asked questions
How many sheets of drywall do I need for a 12×12 room?
With 8-ft walls, the walls are 384 sq ft and the ceiling 144 sq ft. After one door and two windows and 10% waste, you need about 17 sheets of 4×8.
How much area does a sheet of drywall cover?
A 4×8 sheet covers 32 sq ft, 4×10 covers 40 sq ft and 4×12 covers 48 sq ft.
How many screws per sheet?
About 28–32 screws for a 4×8 sheet on walls with studs 16 inches apart — roughly one per square foot. Ceilings need a little closer spacing.
Should I subtract doors and windows?
Yes for large openings, but the offcuts are rarely reusable, which is why a 10–15% waste allowance is still added.