Drywall calculator
Sheets of drywall for a room, from its dimensions, with doors and windows taken out and a waste factor added. The same sheet math the CutOnce app runs on the jobsite.
Updated
Openings use standard sizes: a 3 x 7 ft door (21 sq ft) and a 3 x 5 ft window (15 sq ft). Sheets are rounded up to the whole sheet.
- Wall area
- 384 sq ft
- Openings deducted
- - 36 sq ft
- Net area
- 348 sq ft
- Area with waste
- 383 sq ft
How many sheets of drywall you need
Add the wall area, which is twice the length plus the width, times the ceiling height. Add the ceiling if you are covering it. Subtract the openings, then add a waste factor, and divide by the area of one sheet. A 4x8 sheet is 32 square feet. Round up, because you buy whole sheets.
A worked example
A 12 by 16 ft room with 8 ft walls, one door and two windows, on 4x8 sheets with 10 percent waste. Every number below is computed by the same function that drives the calculator above.
| Wall area (2 x (12 + 16) x 8) | 448 sq ft |
| Openings (1 door + 2 windows) | - 51 sq ft |
| Net area | 397 sq ft |
| Area with 10% waste | 437 sq ft |
| 4x8 sheets (32 sq ft each) | 14 |
Sheets for the same room, by sheet size
A bigger sheet covers more per piece and leaves fewer seams to tape, but it is heavier to hang. The same 12 by 16 ft room needs this many sheets at each US size.
| Sheet size | Area each | Sheets |
|---|---|---|
| 4 × 8 ft | 32 sq ft | 14 |
| 4 × 9 ft | 36 sq ft | 13 |
| 4 × 10 ft | 40 sq ft | 11 |
| 4 × 12 ft | 48 sq ft | 10 |
| 4 × 14 ft | 56 sq ft | 8 |
How to calculate drywall
- 01
Measure the walls
Wall area is twice the length plus the width, times the ceiling height. A 12 by 16 room with 8 ft ceilings is 2 times 28 times 8, which is 448 square feet of wall before openings.
- 02
Take out doors and windows
A standard door is figured at 3 by 7 ft, which is 21 square feet, and a standard window at 3 by 5 ft, which is 15 square feet. Subtracting them keeps you from buying sheets you would only cut away.
- 03
Add waste, then round up
Cuts, offcuts, and the odd broken sheet mean the net area is not what you buy. Ten percent is a common allowance. Divide by the sheet area and round up, because a partial sheet still comes off a full one.
Common questions
- How many sheets of drywall for a 12x16 room?
- With 8 ft walls, one door, two windows, and 10 percent waste, a 12 by 16 ft room takes 14 sheets of 4x8 drywall for the walls. Add the ceiling and it climbs, because the ceiling adds its full length times width in area.
- Does this include screws and joint compound?
- No. This calculator and the app size the sheets and the area, which is the number you buy against. Screws and compound depend on your fastening schedule and how many coats you run, so a single figure would be a guess. Sheet count is the part with one right answer.
- What waste percentage should I use?
- Ten percent is the usual starting point for a plain rectangular room. Go higher for a room with lots of openings, angles, or short walls, where offcuts pile up. Lower only if you are careful and the walls are long and clean.
- Should I subtract doors and windows?
- For an estimate, yes, and this calculator does. It uses standard 3 by 7 ft doors and 3 by 5 ft windows. Some crews skip the deduction on purpose to bank extra material for waste, which is the same as running a higher waste factor.
- Which sheet size should I buy?
- A 4x12 covers more and leaves fewer butt seams to tape, which is why hangers like it on long walls, but it is heavy and hard to move solo. A 4x8 is the one-person default. The table above shows the count either way. This page carries the US sizes; the app also handles the 1200 mm metric sheets used outside North America.
Take off the whole house, offline
The app sizes drywall room by room, keeps the running total, and works with no signal on the jobsite. Part of the one-time toolbox, no subscription.
See also