What to measure
How to use the drywall calculator
Enter the floor’s length and width and the wall height. Choose whether to include the ceiling and pick a sheet size. Keep 10% waste for cuts and breakage.
The formula
- Wall area = 2 × (length + width) × height (+ length × width for the ceiling)
- Sheets = area × (1 + waste) ÷ sheet area (32, 40 or 48 sq ft), rounded up
- Finishing, per square foot of board: 0.009 gal compound, 0.35 ft tape, 1.25 screws
Worked example: 12 × 12 ft room, 8 ft walls
- Walls: 2 × (12 + 12) × 8 = 384 sq ft
- Plus 10%: 422 sq ft ÷ 32 = 13.2 → 14 sheets of 4 × 8
- About 3.5 gallons of compound, 135 ft of tape and 480 screws
Sheet sizes
| Sheet | Area | Notes |
|---|---|---|
| 4 × 8 ft | 32 sq ft | Easiest to carry and hang alone |
| 4 × 10 ft | 40 sq ft | Fits 9–10 ft walls hung vertically |
| 4 × 12 ft | 48 sq ft | Fewest seams; needs two people |
Sheets by room size
With 8 ft walls and 10% extra for waste, openings not subtracted.
| Room | Walls, 4 × 8 | Walls + ceiling, 4 × 8 | Walls + ceiling, 4 × 12 |
|---|---|---|---|
| 10 × 10 ft | 11 | 15 | 10 |
| 10 × 12 ft | 13 | 17 | 11 |
| 12 × 12 ft | 14 | 19 | 13 |
| 12 × 14 ft | 15 | 21 | 14 |
| 14 × 16 ft | 17 | 25 | 17 |
| 16 × 20 ft | 20 | 31 | 21 |
| 20 × 20 ft | 22 | 36 | 24 |
Common mistakes
- Subtracting every door and window. The offcuts rarely fit anywhere else; subtract only very large openings.
- Ordering 4 × 12 sheets without checking the route in. Measure the stairs, halls and doors they have to pass through.
- Leaving out closets, soffits and bulkheads. Measure their walls and add them to the room.
- Ordering the bare area. Keep the extra for cuts and broken corners; a missing sheet costs a second trip.
Frequently asked questions
How many sheets of drywall do I need for a 12x12 room?
With 8 ft walls, the walls are 384 sq ft. Plus 10% waste that's 14 sheets of 4 × 8. Add the ceiling and it's 19 sheets of 4 × 8, or 13 of 4 × 12.
Should I subtract doors and windows?
Usually not. Offcuts from openings rarely fit elsewhere, and the extra covers breakage. Subtract only very large openings like a patio door or garage door.
Which sheet size is best?
Longer sheets mean fewer seams to tape, so pros use 4 × 12 where they can be carried in. 4 × 8 sheets are easiest to handle alone and fit in most vehicles.
How much joint compound per sheet?
About 0.9 gallons of ready-mixed compound per 100 sq ft of board — roughly 0.3 gallons per 4 × 8 sheet.
Is wallboard the same as drywall?
Yes. Wallboard, drywall, gypsum board and plasterboard are names for the same gypsum panel, and Sheetrock is a brand of it. The sheet count is the same whichever name your store uses.
How many sheets of drywall for a 10x10 room?
With 8 ft walls and 10% waste, 11 sheets of 4 × 8 for the walls. With the ceiling it's 15 sheets of 4 × 8, or 10 sheets of 4 × 12.
How many screws per sheet of drywall?
At 1.25 screws per square foot, about 40 screws for a 4 × 8 sheet and 60 for a 4 × 12 sheet.
How much joint compound for a 20x20 room?
With 8 ft walls and the ceiling, that's 1,040 sq ft of board, about 9.4 gallons of compound, 364 ft of tape and 1,300 screws. Walls only take about 5.8 gallons.
Sources
Formulas and defaults last reviewed October 30, 2026. How we check our math.