Drywall Calculator
Calculate how many sheets of drywall (4×8 or 4×12) you need for walls and ceilings, subtracting doors and windows.
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Extended More scenarios, charts & detailed breakdown ▾
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How to Use This Calculator
- Enter the room dimensions and ceiling height.
- Enter the number of doors and windows.
- Select sheet size and whether to include the ceiling.
- Results show sheets needed for walls and ceiling separately.
Formula
Wall area = 2(L+W)×H − doors×20 − windows×15
Sheets = ceil(Total area ÷ Sheet area × (1 + waste%))
Example
Example: 12×14 ft room, 9 ft ceiling, 1 door, 2 windows → Wall area 448 sq ft → 16 sheets of 4×8 (10% waste).
Frequently Asked Questions
- Calculate total wall area (perimeter × wall height), add ceiling area if applicable, then subtract openings (doors and windows). Divide the net area by the sheet area and add a waste factor. A standard 4×8 sheet covers 32 sq ft; a 4×12 sheet covers 48 sq ft. For example: a 12 × 14 ft room with 9 ft ceilings has a wall perimeter of 52 ft × 9 ft = 468 sq ft walls + 168 sq ft ceiling = 636 sq ft. Minus 2 doors (2 × 20 = 40 sq ft) and 2 windows (2 × 15 = 30 sq ft) = 566 sq ft. Add 10% waste = 623 sq ft ÷ 32 = 20 sheets (round up).
- 4×8 drywall sheets (32 sq ft) are the most common, easiest to carry alone, and fit through standard doorways. They are the best choice for DIY projects. 4×12 sheets (48 sq ft) reduce the number of horizontal seams on walls with 9-foot ceilings, producing a smoother final finish — but they require two people to handle and may not fit through narrow doorways. Professionals prefer 4×12 or even 4×16 on high ceilings. Use the larger sheets where minimizing seams is a priority, and use 4×8 in tight spaces or when working solo.
- Add 10% waste for simple rectangular rooms with standard door and window placements. Rooms with many inside and outside corners, L-shapes, or irregular layouts warrant 15% waste. Complex ceilings with angles, vaults, or built-in soffits can require 20% extra. The waste mainly comes from cutouts around electrical boxes, windows, and doors, plus miscuts and damaged corners during transport. Drywall is inexpensive, so buying one or two extra sheets is a very cheap insurance policy against running short during finishing.
- The calculator deducts the area of each opening from the total wall area. A standard interior door opening is approximately 20 sq ft (3 ft wide × 6.67 ft tall). A standard window opening is approximately 15 sq ft (3 ft wide × 5 ft tall). Enter the number of each type of opening and the calculator deducts them automatically. For oversized windows, French doors, or garage doors, calculate the actual opening area and enter it in the custom deduction field in the professional tier. Do not deduct openings from your ceiling area.
- Yes — the ceiling option adds the ceiling area (length × width of the room) to the total drywall calculation. Ceilings are almost always finished with drywall in residential construction. Note that ceiling drywall is typically installed with the sheets running perpendicular to the ceiling joists and may require different butt joint scheduling than walls. Ceilings require more labor than walls because you are working overhead. For large ceilings, a drywall lift tool is highly recommended to support the sheet while fastening.