How to calculate drywall
Start with the total surface area you're covering: the walls (perimeter times ceiling height) plus the ceiling if you're hanging that too. Divide by the area of one sheet — 32 square feet for a 4×8, 48 for a 4×12 — and add a waste allowance for cuts around doors, windows, and outlets. This calculator runs that math and also estimates the consumables most people forget to buy.
Don't forget the consumables
Hanging the board is only half the job. You'll also need screws (roughly three dozen per sheet), joint compound to fill the seams and screw heads, and paper or mesh tape for every joint. As a rough guide, plan about a gallon of compound and 40 linear feet of tape per 100 square feet — more if your layout has lots of seams.
4×8 vs. 4×12 sheets
Longer sheets mean fewer seams to tape and a cleaner finished wall, but they're heavy and awkward to maneuver up stairs or in small rooms. Shorter 4×8 sheets are far easier to handle solo. Pick based on the room and whether you have a helper.
Frequently asked questions
Should I subtract doors and windows?
For a quick estimate, the 10% waste allowance roughly offsets normal openings. If a room has unusually large windows or openings, you can lower your area input accordingly.
What thickness of drywall?
Half-inch is standard for walls and ceilings in most homes; 5/8-inch is used where fire rating or sag resistance matters. Thickness doesn't change the sheet count, only the product you buy.
How much does drywall cost?
Enter your price per sheet for a material estimate. Compound, tape, and screws add a modest amount on top; labor is the bigger cost if you hire a finisher.
Drywall calculation example
A 12-by-12-foot room with 8-foot ceilings has 384 square feet of wall area before subtracting openings. Adding a 10% allowance gives about 423 square feet, so the walls require roughly fourteen 4-by-8 sheets. Include the ceiling separately if it will also be drywalled.
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Complete the estimate with the paint calculator, tile calculator, or air-conditioner BTU calculator.