How do I calculate drywall for a room?
Wall area = 2 × ceiling height × (length + width). Subtract about 20 sq ft per door and 15 sq ft per window. Divide by sheet size (32 sq ft for 4×8) and add waste.
Drywall Calculator
Drywall is sold by the sheet — but you buy based on wall area. Enter room length, width, and ceiling height and we convert perimeter × height into whole 4×8 or 4×12 sheets with waste included.
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Project settings
Default 4×8 ft (32 sq ft)
Default 10% for cuts and mistakes
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How wall area is calculated
For a rectangular room, wall area = 2 × ceiling height × (length + width). A 12×12 room with 8 ft ceilings has 384 sq ft of wall — before deducting doors and windows.
Toggle ceiling drywall in project settings to add length × width on top of wall area. Use our ceiling drywall calculator when walls and ceiling are separate purchases.
Sheet sizes and waste
Standard 4×8 sheets cover 32 sq ft; 4×12 sheets cover 48 sq ft and reduce horizontal seams on long walls. Most DIYers add 10% waste for cuts and mistakes — increase to 12–15% for rooms with many corners or niches.
Need a quick sheet count without re-entering dimensions? Jump to how many drywall sheets for the same math with a sheet-first framing.
Before you order at the lumber yard
Match sheet thickness to your application — 1/2 inch is typical for walls; some ceilings require 5/8 inch for fire rating. Count screws, joint compound, and tape separately — this tool focuses on sheet quantity only.
Frequently asked questions
How much waste should I add for drywall?
Most DIYers add 10% extra for cuts, mistakes, and future patches. Complex layouts with many corners may need 12–15%.
What size drywall sheets should I use?
Standard 4×8 ft sheets cover 32 sq ft each. 4×12 ft sheets cover 48 sq ft and reduce seams on long walls — enter your sheet size in settings.
Related calculators
Drywall Calculator · https://drywall-calculator.com/drywall-calculator/