Drywall Calculator
Enter your total wall area and a waste allowance to estimate how many standard 4×8 drywall sheets to buy.
Last updated: September 5, 2026
Frequently asked questions
How many sheets of drywall do I need for 400 sq ft of wall?
At a 10% waste allowance, 400 sq ft needs about 14 standard 4×8 ft sheets (32 sq ft each).
Why do I need extra drywall for waste?
Cuts around outlets, corners, doorways, and windows use extra material - a 10% allowance keeps you from running short mid-job.
What size drywall sheets are standard?
4×8 feet (32 sq ft) is the most common size for walls and ceilings, though 4×12 sheets are also used on larger walls to reduce the number of seams - this calculator assumes the standard 4×8 sheet unless you adjust the coverage value.
Should I calculate drywall separately for walls and ceilings?
Yes - ceilings often use thicker or fire-rated drywall in some rooms, and calculating them separately from walls avoids mixing different sheet requirements into one number. Measure ceiling square footage and wall square footage independently, then run each through the calculator.
How many sheets do I need for a 12×20 ft room with 8 ft ceilings?
Wall area is the perimeter times the ceiling height: (12+20)×2×8 = 512 sq ft. With a 10% waste allowance that's 563.2 sq ft, which at 32 sq ft per 4×8 sheet rounds up to 18 sheets.
Should I subtract door and window openings from the wall area?
For average-size doors and windows, most estimators skip subtracting them since the 10% waste allowance already covers the material lost cutting around framing. For unusually large openings, like sliding doors or picture windows, subtract that area from your wall total first.
Does sheet count change between 1/2 inch and 5/8 inch drywall?
No - sheet count is based on square footage of coverage, not thickness, so the calculation is the same either way. What changes is weight and, in some cases, code requirements: 5/8 inch fire-rated drywall is often required for garages and shared walls between units.