Walls & Drywall
Drywall Calculator
Work out how many drywall sheets a room needs, walls or walls and ceiling, with an allowance for waste.
Calculate your drywall
Room measurements in feet. This estimates sheets only — screws, tape and joint compound vary too much by product and finish to estimate reliably. The estimate updates as you type.
The method
- 01
Wall area
2 × (length + width) × wall height
Room length and width give the perimeter; wall height turns that into wall area.
- 02
Add the ceiling, if boarding it
wall area + (length × width)
Only needed if you're boarding the ceiling as well as the walls.
- 03
Subtract openings
gross area − door and window areas
There's no assumed door or window size — measure each one and add it above with "Add a door" or "Add a window".
- 04
Add a waste allowance
net area × (1 + waste allowance)
Covers offcuts and mistakes. The calculator above defaults to 10%, but 0% is fine if you'd rather round manually.
- 05
Sheets to buy
round up (area with waste ÷ sheet coverage)
Rounds up to the next whole sheet, because sheets are purchased as whole sheets. A 4×8 sheet covers 32 sq ft; a 4×12 sheet covers 48 sq ft.
Worth knowing
- This estimates sheets only — screws, joint tape and joint compound depend too much on framing spacing, taping method, finish level and product yield to estimate reliably from geometry alone.
- Larger sheets mean fewer joints to tape and finish, but they're heavier and harder to maneuver alone.
- This covers a single rectangular room. For an irregular room, measure each wall segment's real length, multiply each by the wall height and add those results together; work out the ceiling area separately. Don't count any imaginary dividing line you drew across the floor — it isn't a wall, and boarding area along it doesn't exist.
Drywall calculator example
- Room
- 12 × 10 ft
- Wall height
- 8 ft
- Ceiling
- Included
- Door
- 3 × 7 ft
- Wall area2 × (12 + 10) × 8 = 352 sq ft
- Ceiling area12 × 10 = 120 sq ft
- Gross area352 + 120 = 472 sq ft
- Subtract the door472 − 21 = 451 sq ft
- After 10% waste451 × 1.10 = 496.1 sq ft
- 4×8 sheets (32 sq ft each)496.1 ÷ 32 = 15.5 → 16
You need 16 sheets.
Before waste, the room itself needs 14.09 sheets — the extra covers offcuts and mistakes.
4×8 vs. 4×12 sheets
Both are standard stocked sizes — the right choice is mostly about the wall itself, not the math.
A 4×8 ft sheet is the easier size to handle alone and fits through most doorways and stairwells without trouble. A 4×12 ft sheet covers more per sheet and means fewer seams to tape and finish on a tall wall or a long run, but it's heavier and usually a two-person job to hang. Either works with the calculator above — just match the sheet size to what you're actually buying.
Should you include the ceiling?
Only turn this on if you're actually boarding the ceiling in the same job.
Leave "Include the ceiling" off if you're only boarding the walls — a repair, a partition, or a room where the ceiling is already finished. Turn it on for a new room or a full gut, where the ceiling needs sheets as well. The calculator adds the ceiling's length × width to the wall area before working out sheets, so it's counted once, not twice.
How much waste allowance to use
A waste allowance covers offcuts around doors, windows and corners, plus the odd damaged sheet.
| Situation | Typical waste allowance |
|---|---|
| Straightforward rectangular room, few openings | Around 5–10% may be a useful planning range |
| Typical room with several openings or corners | Around 10% is a common planning starting point |
| Irregular layout, many openings, or a first-time install | 10–15% or more may be appropriate, depending on the layout |
Important: these are planning guidelines, not guarantees. The right allowance depends on the room's shape, how many cuts the openings and corners force, the sheet size, and how much gets damaged in handling. 0% is a valid choice if you'd rather round up manually after seeing the exact figure.