Short answer: A standard 12×12 room with 8-foot ceilings needs 18 sheets of 4×8-foot drywall — 16 sheets to cover the walls and ceiling, plus 2 extra for cuts, mistakes, and waste. The formula is simple: add up the wall and ceiling area, subtract the door and window openings, divide by 32 (the area of one 4×8 sheet), then add 10%.
How the drywall calculation works
A 12×12 room has a perimeter of 48 feet. Multiply by the 8-foot ceiling height and the walls total 384 square feet. The ceiling adds another 144 square feet (12 x 12), for 528 square feet in total. Subtract one standard door (21 sq ft) and one window (15 sq ft) and you get 492 square feet of drywall to cover. Divide by 32 square feet per 4×8 sheet: 492 / 32 = 15.4, so round up to 16 sheets. Add the standard 10% waste allowance: 16 x 1.10 = 17.6, so buy 18 sheets.
Drywall sheets by room size
| Room | Net wall + ceiling area | Sheets of 4×8 drywall (10% waste included) |
|---|---|---|
| 10×10 room | 384 sq ft | 14 sheets |
| 12×12 room | 492 sq ft | 18 sheets |
| 14×16 room | 668 sq ft | 24 sheets |
| 16×20 room | 860 sq ft | 30 sheets |
(All assume 8-foot ceilings, walls plus ceiling, one door and one window subtracted.)
What about 4×12 sheets?
A 4×12 sheet covers 48 square feet, so the same 12×12 room needs 492 / 48 = 10.25, rounded up to 11 sheets, plus 10% waste, which is 13 sheets. Longer sheets mean fewer seams on long walls, but they are heavier and harder to handle alone, so most DIY jobs stick with 4×8 sheets.
How many screws and how much mud?
Plan on about 28 screws per 4×8 sheet, so 18 sheets need about 500 screws — buy a 5-pound box and you will have plenty. For joint compound, one 5-gallon bucket covers roughly 400 to 500 square feet of drywall surface, so one bucket handles this room, with a spare gallon for touch-ups.
Frequently asked questions
How many drywall sheets do I need for a 12×12 room?
18 sheets of 4×8 drywall, counting the walls and the ceiling with 8-foot ceilings and a 10% waste allowance.
Do I subtract doors and windows?
Yes. A standard door is 21 square feet and a window is about 15 square feet. Subtracting them saves 1 to 2 sheets on a typical room.
Should I count the ceiling?
Yes, if you are drywalling it. The ceiling of a 12×12 room is 144 square feet, about 5 sheets. If the ceiling is already finished, count the walls only: 348 square feet needs 11 sheets plus 10% waste, so 13 sheets.
Is 10% waste enough?
Yes for rectangular rooms. For rooms with lots of angles, niches, or soffits, use 15% instead.
Work out your exact number before you buy with our drywall calculator.