Drywall is bought in whole sheets, and running out halfway through a room means another trip with a truck or roof rack. This calculator works out the wall and ceiling area of a rectangular room, adds a waste allowance and converts it to sheets of 4 × 8, 4 × 10 or 4 × 12 ft gypsum board.
How to use the drywall calculator
- Enter the room's length, width and wall height.
- Choose whether to include the ceiling.
- Pick a sheet size. 4 × 8 is the easiest to handle; longer sheets mean fewer seams.
- Keep about 10% waste for cutouts, damaged corners and pieces that don't fit elsewhere.
The result shows the wall area, ceiling area and total, plus the sheets to buy.
Drywall formula
Ceiling area = L × W
Sheets = ⌈ (wall area + ceiling area) × (1 + waste% ÷ 100) ÷ sheet area ⌉
Sheet areas: 4 × 8 = 32 sq ft, 4 × 10 = 40 sq ft, 4 × 12 = 48 sq ft. Doors and windows are not subtracted — sheets are hung over openings and cut out, and those offcuts are part of the waste allowance.
Worked example: a 12 × 12 ft bedroom
- Walls: 2 × (12 + 12) × 8 = 384 sq ft
- Ceiling: 12 × 12 = 144 sq ft
- Total with 10% waste: 528 × 1.10 = 580.8 sq ft
- 4 × 8 sheets: 580.8 ÷ 32 = 18.2 → 19 sheets
- 4 × 12 sheets: 580.8 ÷ 48 = 12.1 → 13 sheets
Drywall sheets by room size
8 ft walls, 10% waste.
| Room | Wall area | Ceiling area | 4×8 sheets, walls only | 4×8 sheets, walls + ceiling | 4×12 sheets, walls + ceiling |
|---|---|---|---|---|---|
| 10 × 10 ft | 320 | 100 | 11 | 15 | 10 |
| 10 × 12 ft | 352 | 120 | 13 | 17 | 11 |
| 12 × 12 ft | 384 | 144 | 14 | 19 | 13 |
| 12 × 14 ft | 416 | 168 | 15 | 21 | 14 |
| 14 × 16 ft | 480 | 224 | 17 | 25 | 17 |
| 16 × 20 ft | 576 | 320 | 20 | 31 | 21 |
Planning tips
- Hang ceilings first, then walls, so the wall sheets support the ceiling edges.
- Run sheets horizontally on walls in most rooms with 8 ft ceilings: two 4 ft sheets stacked cover the height with one seam at a comfortable working height.
- Use moisture-resistant board in bathrooms and cement board behind tile in showers.
- Check access. 4 × 12 sheets may not make it up a narrow staircase.
Once the walls are finished, the Paint Calculator works out primer and paint. For accent walls with trim, see the Board and Batten 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 — 528 sq ft in all. Adding 10% waste gives 581 sq ft, which is 19 sheets of 4 × 8 or 13 sheets of 4 × 12.
Should I subtract doors and windows from drywall?
Usually not. Installers hang full sheets over most openings and cut them out, and the offcuts rarely fit elsewhere. Subtract only very large openings such as patio doors or wide archways.
Is 4×8 or 4×12 drywall better?
Longer sheets mean fewer joints to tape and finish, so 4 × 12 is popular with pros on walls and ceilings. 4 × 8 sheets are lighter and easier to carry and hang alone, and fit in more vehicles.
How much does a sheet of drywall cover?
A 4 × 8 sheet covers 32 sq ft, a 4 × 10 covers 40 sq ft and a 4 × 12 covers 48 sq ft.
What thickness of drywall should I use?
1/2 in is standard for interior walls in houses; 5/8 in is common for ceilings and fire-rated assemblies. Your local code may require specific types, for example fire-rated board between a garage and living space.