Formula
Area = 2 × (length + width) × height (+ length × width for the ceiling)Sheets = area × (1 + waste) ÷ sheet area, rounded up How it works
Add up the wall area — the room’s perimeter times its height — and the ceiling if you are hanging that too, then divide by the area of one sheet. A 4 × 8 sheet covers 32 ft², a 4 × 10 covers 40 ft² and a 4 × 12 covers 48 ft².
Pros usually do not subtract doors and windows from the count: the offcuts are rarely reusable and the extra covers mistakes. The waste allowance handles cutting losses; 10% is typical, more for rooms with many corners or a vaulted ceiling.
Longer sheets mean fewer butt joints to tape and a flatter finish, but they are heavy and awkward to carry up stairs. Use ½-inch board for walls and ⅝-inch or sag-resistant ½-inch for ceilings, and check local code for fire-rated Type X where required.
Frequently asked questions
How many sheets of drywall for a 12 × 12 room?
With 8 ft walls: 384 ft² of walls plus 144 ft² of ceiling is 528 ft². With 10% waste that is 581 ft², or 19 sheets of 4 × 8.
How much joint compound and tape do I need?
A rough rule is one 4.5-gallon bucket of all-purpose compound and one 500 ft roll of tape for every 15–20 sheets.