Drywall Calculator
Free drywall calculator. Estimate how many 4x8 or 4x12 drywall sheets you need for any room, with openings and waste accounted for.
A drywall calculator estimates how many sheets cover a room’s walls and ceiling, subtracts door and window openings, and adds a cutting allowance. It supports 4 × 8 ft and 4 × 12 ft sheets.
How sheets are counted
The calculator builds the area, removes the openings, then divides by the sheet size and rounds up:
wall area = 2 × (length + width) × heightceiling area = length × width(included by default)net area = wall area + ceiling area − openingssheets = ceil(net area ÷ sheet area), thensheets with waste = ceil(sheets × 1.10)
The 10% waste factor is fixed in the tool. It covers cuts around openings, odd corners, and the occasional spoiled sheet. A 4 × 8 sheet covers 32 ft²; a 4 × 12 sheet covers 48 ft².
Worked example: a 12 × 10 ft room with 8 ft walls
Defaults: length 12 ft, width 10 ft, height 8 ft, 4 × 8 sheets, no openings, ceiling included.
| Step | Calculation | Result |
|---|---|---|
| Wall area | 2 × (12 + 10) × 8 | 352 ft² |
| Ceiling area | 12 × 10 | 120 ft² |
| Net area | 352 + 120 − 0 | 472 ft² |
| Sheets, no waste | 472 ÷ 32 = 14.75, round up | 15 sheets |
| Sheets with 10% waste | 15 × 1.10 = 16.5, round up | 17 sheets |
Buy 17 and return any unopened sheets. Sheets are inexpensive relative to a second trip, and the waste figure assumes normal cuts, not a room full of angled walls.
Reference: sheets by room size
Assuming 8-foot walls, the ceiling included, no openings, and 4 × 8 sheets.
| Room (ft) | Wall area | Net with ceiling | Sheets | +10% waste |
|---|---|---|---|---|
| 10 × 10 | 320 ft² | 420 ft² | 14 | 16 |
| 12 × 10 | 352 ft² | 472 ft² | 15 | 17 |
| 12 × 12 | 384 ft² | 528 ft² | 17 | 19 |
| 14 × 12 | 416 ft² | 584 ft² | 19 | 21 |
| 16 × 14 | 480 ft² | 704 ft² | 22 | 25 |
Subtract a large opening by entering its combined area in the doors/windows field. A standard door is about 21 ft² and a typical window 15 ft², so a room with two doors and three windows carries roughly 87 ft² of openings.
Measuring the room correctly
Measure the longest point of each wall, not an average, and take wall height from finished floor to ceiling rather than up to the joists. Because the calculator assumes a simple rectangle, split an L-shaped room into two rectangles, run each, and add the sheets. Bay windows and angled walls are easier to handle by measuring the wall area directly and entering the openings as you go. Small closets and returns still consume board, so include them.
Common mistakes
- Forgetting the ceiling. It is the same material and roughly the floor area — often a third of the job.
- Buying with no waste. Cuts around openings and imperfect corners eat 10–15% of a sheet order.
- Leaving openings in the total. Doors and windows are not wall; subtract them or you overbuy.
- Mixing sheet sizes mid-count. Stick to one size for the whole job so seams and counts stay consistent.
How many drywall sheets for a 12 × 10 room?
About 472 ft² of wall plus ceiling, which is 15 sheets of 4 × 8 and 17 once the 10% waste allowance is added.
Should I use 4 × 8 or 4 × 12 sheets?
A 4 × 12 covers more area with fewer seams, which means less taping, but it is heavier and awkward to hang alone. For 8-foot walls, 4 × 8 sheets run vertically with no butt joints.
How much joint compound and tape will I need?
A rough guide is one box of screws per 4–5 sheets, one roll of tape per 10–12 sheets, and about one bag of joint compound per 4–6 sheets. Those are estimates, not outputs of this calculator.
What thickness of drywall should I use?
Half-inch is standard for walls and ceilings in most homes, while 5/8-inch is used where fire rating or extra stiffness matters, such as a garage ceiling. This calculator counts sheets, not thickness, so choose the board before you order.
The same room measurements feed the paint calculator for the finish coat, and the insulation R-value calculator if you are filling the cavities before hanging board.