Drywall Calculator
Determine how many drywall sheets you need to cover all walls and the ceiling of a room, with automatic deductions for doors and windows. Great for budgeting before any renovation or new build.
About this calculator
Drywall quantity is found by computing the total surface area of a room—all four walls plus the ceiling—then subtracting the area occupied by doors and windows, and finally dividing by the area of a single drywall sheet. Wall area is calculated as the perimeter of the room multiplied by ceiling height: 2 × (roomLength + roomWidth) × ceilingHeight. Ceiling area is roomLength × roomWidth. Each door or window opening is approximated at 20 sq ft. The complete formula is: Sheets = ⌈(2 × (roomLength + roomWidth) × ceilingHeight + roomLength × roomWidth − doorWindows × 20) ÷ sheetSize⌉. Standard 4×8 sheets cover 32 sq ft; 4×12 sheets cover 48 sq ft. Rounding up ensures you always have enough material to complete the job without a second trip to the supplier.
How to use
Consider a room 12 ft long, 10 ft wide, with 9 ft ceilings, 2 doors and windows combined, using standard 4×8 sheets (32 sq ft each). Wall area: 2 × (12 + 10) × 9 = 2 × 22 × 9 = 396 sq ft. Ceiling area: 12 × 10 = 120 sq ft. Opening deductions: 2 × 20 = 40 sq ft. Net area: 396 + 120 − 40 = 476 sq ft. Sheets needed: ⌈476 ÷ 32⌉ = ⌈14.875⌉ = 15 sheets. You would purchase 15 sheets of 4×8 drywall.
Frequently asked questions
What size drywall sheets should I use for walls versus ceilings?
For walls, 4×8 ft sheets (32 sq ft) are the most common and easiest to handle solo, though 4×12 sheets (48 sq ft) reduce the number of seams on tall walls. For ceilings, many professionals prefer 4×12 or even 4×16 sheets because fewer seams mean less taping and finishing work overhead. Thicker 5/8-inch drywall is required by code for garage ceilings attached to living spaces for fire resistance. Standard wall drywall is typically 1/2 inch thick in residential construction.
How much joint compound and tape do I need for a drywall job?
A general rule of thumb is one gallon of pre-mixed joint compound (mud) per 100 square feet of drywall. For tape, figure approximately 370 linear feet of paper tape per 500 sq ft of drywall—roughly one roll per average room. You will also need corner bead for all outside corners. Most drywall jobs require three coats of compound: a taping coat, a filler coat, and a finish coat, with light sanding between each.
Why do I need to deduct door and window areas from my drywall calculation?
Doors and windows are framed openings in the wall where no drywall is installed, so counting them inflates your sheet count and wastes money. This calculator deducts 20 sq ft per opening as a standard approximation that works well for typical residential doors and windows. For unusually large windows or double doors, you may wish to measure the actual rough opening and adjust. Even with deductions, many contractors still add a 10% overage buffer to account for cuts, waste, and damaged sheets during installation.