Drywall Calculator
Estimating drywall for a room requires calculating wall area and ceiling area separately and then subtracting openings for doors and windows. This drywall calculator takes the room perimeter in feet, the ceiling height, and the ceiling area (length x width) to compute total wall square footage. Standard doors are subtracted at 21 square feet each and standard windows at 15 square feet each. A 10% waste factor is applied to the total before dividing by 32 (the square footage of one 4x8 sheet) to give the number of panels needed. The tool separates wall sheets from ceiling sheets, since some installers use different panel sizes for each. Drywall is sold in 4x8, 4x10, 4x12, and 4x16 panels; this calculator uses 4x8 as the default. When hanging drywall on ceilings, many contractors prefer 4x12 panels to span three joists at 16-inch centres, which reduces seams. For walls framed at 16-inch centres in rooms with 8-foot ceilings, vertical 4x8 panels typically eliminate horizontal seams. For rooms taller than 8 feet, horizontal installation with a butt joint at mid-wall is common. Always buy from the same manufacturer lot to ensure consistent thickness and colour. Stack panels flat for storage; do not store them on edge unsupported as they can warp or break under their own weight.
Drywall calculation formula
Wall area = Perimeter x Ceiling height - (Doors x 21) - (Windows x 15)
Total area = (Wall area + Ceiling area) x 1.10
Sheets = ceil(Total area / 32)
Worked example: 12 x 12 ft room (perimeter 48 ft), 8 ft ceiling, 1 door, 2 windows
- Wall area: 48 x 8 = 384 sq ft
- Subtract: 384 - 21 - 30 = 333 sq ft net wall area
- Ceiling: 12 x 12 = 144 sq ft
- Total with 10% waste: (333 + 144) x 1.10 = 524.7 sq ft
- Sheets: ceil(524.7 / 32) = 17 sheets
Drywall calculator: frequently asked questions
How many square feet does a 4x8 drywall sheet cover?
A standard 4x8 foot drywall panel covers 32 square feet. This calculator divides your total drywall area (including waste) by 32 to give you the number of 4x8 sheets to purchase. Some installers prefer 4x12 panels for tall walls or ceilings to reduce seams; those cover 48 square feet each.
How much waste should I allow for drywall?
A 10% waste factor is standard for most residential drywall jobs. For rooms with many windows, doors, or irregular shapes, 12 to 15% is more appropriate. Waste comes from cutting around outlets, switches, doors, and windows, and from panels that break or crack during handling. Always round up to the nearest whole sheet.
How much drywall joint compound do I need?
A general rule is one gallon of ready-mixed joint compound per 100 square feet of drywall. For a full three-coat finish (tape coat, bed coat, finish coat), you may need 1.5 to 2 gallons per 100 square feet. Joint compound is sold in 1-gallon, 3.5-gallon, and 4.5-gallon buckets. Pre-mixed compound is easiest to use; dry compound mixed with water is lighter to transport.
How many screws do I need to hang drywall?
Use drywall screws spaced 12 inches apart on ceiling panels and 16 inches apart on walls, driven into every stud and joist. A rough estimate is 1 pound of 1-5/8 inch drywall screws per 500 square feet of drywall. Screws are far superior to nails because they do not pop out as lumber dries and shrinks.
What thickness of drywall should I use?
The most common residential drywall thickness is 1/2 inch (12.7 mm), which is suitable for most walls and ceilings. For ceilings in new construction, 5/8 inch drywall sags less and provides better fire resistance. For garage walls that share a wall with the house interior, 5/8 inch type X fire-rated drywall is typically required by building code. For curved walls or radius applications, 1/4 inch drywall is used.
Sources
- US Gypsum Association GA-216 application guide: gypsum.org.
- IRC Section R702 Interior wall and ceiling finish requirements: codes.iccsafe.org.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology. Check local building codes for fire-rated requirements.