How much drywall you need
Drywall estimates start with the surface area, but the details decide whether you make one trip to the store or three: ceilings, doors and windows, sheet length and waste. The calculator measures the walls and optional ceiling of a rectangular room, subtracts standard openings, adds a waste margin and gives the number of sheets, screws, joint compound and tape, with the cost.
The formulas
- Wall area = 2 × (length + width) × height
- Ceiling area = length × width
- Net area = walls + ceiling − 21 sq ft per door − 15 sq ft per window
- Sheets = net area × (1 + waste) ÷ sheet area, rounded up
- Screws: about one per square foot
- Joint compound: about 1 gallon of ready-mix per 100 sq ft
- Tape: about 370 ft per 1,000 sq ft
Worked example
A 12 × 14 ft bedroom with 8 ft walls, a ceiling, one door and two windows, using 4 × 8 sheets.
- Walls: 2 × (14 + 12) × 8 = 416 sq ft; ceiling: 168 sq ft.
- Openings: 21 + 2 × 15 = 51 sq ft, so the net area is 533 sq ft.
- With 10% waste: 586 sq ft ÷ 32 = 18.3, so 19 sheets, about $285 at $15 each.
- You also need about 530 screws, 5.3 gallons of joint compound (one 4.5 gallon box plus a smaller one) and one 250 ft roll of tape.
Choosing sheets
| Sheet | Area | Best for |
|---|---|---|
| 4 × 8 ft | 32 sq ft | Easy to handle, fits in most vehicles |
| 4 × 10 ft | 40 sq ft | 9 and 10 ft walls installed vertically |
| 4 × 12 ft | 48 sq ft | Fewer butt joints on long walls and ceilings |
Thickness: 1/2 in is standard for walls; 5/8 in for ceilings with joists at 24 in on center and for fire-rated assemblies, such as the wall between a garage and the house. Use moisture-resistant board behind bathroom tile, or better, a cement board.
Tips for a cleaner job
- Hang ceilings first, then walls, with the upper sheet tight to the ceiling.
- Run sheets horizontally on walls up to about 9 ft: it reduces the joint length and puts the factory taper at a comfortable height.
- Stagger butt joints and keep them away from door and window corners, where cracks start.
- Drive screws just below the surface without breaking the paper, about 3/8 in from the edges.
- Plan three coats of compound: tape coat, fill coat and finish coat, sanding lightly between them.