How to use the drywall calculator
- Measure each room: length, width and wall height from floor to ceiling. Type feet and inches, so 8 ft 6 in goes in as 8 and 6.
- Count the doors and windows in that room. Their sizes are set once, below the rooms. A door of 3 x 7 ft and a window of 3 x 4 ft are filled in as defaults, so change them to your real sizes.
- Tick Ceiling too if you are hanging the ceiling as well.
- Pick a sheet size: 4 x 8, 4 x 10 or 4 x 12 ft, or Other size to type the size of the sheet you will buy.
- Set the waste. 10% is filled in. It is a common allowance, not a rule: raise it for rooms with many corners and cut-outs.
For a whole house, press Add another room for each room. The result shows sheets for walls and for ceilings separately, the square feet of drywall, and joint compound and tape from USG's published figures. Choose Meters to measure in meters and centimeters.
How many sheets of drywall do I need?
The drywall calculator works in square feet, the same way you would on paper:
- Wall area = 2 x (length + width) x height, the distance around the room times the height.
- Take off each door and window: count x width x height.
- Ceiling area = length x width.
- Add the waste: area x (1 + waste / 100).
- Divide by the area of one sheet (32 sq ft for 4x8) and round up. Walls and ceiling are rounded up separately, so each count stands on its own.
Here is a 12 x 12 ft bedroom with 8 ft walls, one door, one window and the ceiling, in 4x8 sheets with 10% waste. Press Try an example to see it in the calculator.
| Step | Working | Result |
|---|---|---|
| Wall area | 2 x (12 + 12) x 8 | 384 sq ft |
| Door and window | 3 x 7 + 3 x 4 | -33 sq ft |
| Walls to cover | 384 - 33 | 351 sq ft |
| Ceiling | 12 x 12 | 144 sq ft |
| Wall sheets | 351 x 1.10 / 32 = 12.07 | 13 sheets |
| Ceiling sheets | 144 x 1.10 / 32 = 4.95 | 5 sheets |
| Total | 18 sheets |
The total drywall area is 495 sq ft, or 544.5 sq ft with waste. USG's own Sheetrock Wallboard Estimator notes: "This estimate doesn't include an allowance for waste." That is why the waste is a separate, editable figure here.
4x8 vs 4x12 drywall
Sheets come 4 ft wide in several lengths. USG's product page for one of its standard panels lists "48 in. x 8 - 16 ft.", so 8, 10 and 12 ft lengths are all made. The same room needs fewer of the longer sheets:
| Sheet | Area | Walls | Ceiling | Total |
|---|---|---|---|---|
| 4 x 8 ft | 32 sq ft | 13 | 5 | 18 |
| 4 x 10 ft | 40 sq ft | 10 | 4 | 14 |
| 4 x 12 ft | 48 sq ft | 9 | 4 | 13 |
Fewer sheets means fewer joints to tape. Longer sheets are heavier to carry and harder to get up stairs, so 4x8 can suit small rooms and 4x12 suits walls and ceilings long enough to use the full length. The count here is by area: it assumes offcuts get used elsewhere, so a room with many short wall sections can need a sheet or two more.
Drywall calculator for a whole house
Add each room and the calculator adds up the walls and the ceilings, then rounds up once for the whole job. This example has three rooms with 8 ft walls and ceilings, using the default door and window sizes:
| Room | Doors, windows | Walls | Ceiling |
|---|---|---|---|
| 12 x 12 ft | 1, 1 | 351 sq ft | 144 sq ft |
| 11 x 10 ft | 1, 1 | 303 sq ft | 110 sq ft |
| 16 x 14 ft | 2, 3 | 402 sq ft | 224 sq ft |
| Total | 1,056 sq ft | 478 sq ft |
With 10% waste that is 37 sheets of 4x8 for the walls and 17 for the ceilings, 54 in all, or 36 sheets of 4x12. Working each room out on its own and adding the rounded counts gives 55 sheets of 4x8, one more, because each room rounds up separately.
Joint compound and tape
The compound and tape figures use the drywall area before waste, and come from USG's own published guidance:
- Tape. USG's submittal sheet for its paper joint tape gives "Coverage: Approx. 370 ft. per 1,000 sq. ft. (112 m/93 m2) gypsum panels." The same sheet lists rolls of 75, 250 and 500 ft; the calculator counts 250 ft rolls.
- Joint compound. USG says to expect "approximately two 4.5 gallon pails" of its UltraLightweight All Purpose compound "to finish 1000 sq. ft. of gypsum wallboard", and that "The coverage rate is comparable to other USG ready-mix joint compounds." So the calculator uses 9 gallons per 1,000 sq ft.
For the 12 x 12 ft room, 495 sq ft of board needs about 183 ft of tape and 4.5 gallons of compound: one 250 ft roll and one 4.5 gallon pail. Other brands and powder compounds differ, so check the coverage on the product you buy.
Drywall screws
The calculator does not count screws, because the makers we checked publish spacing, not a number per sheet. USG gives this spacing for walls and ceilings that are not fire-rated: When screwing into wood and steel framing the spacing is 12 inches on ceilings and 16 inches for walls.
For nails it gives 7 inches on ceilings and 8 inches on walls. USG adds that fire-rated walls follow the fastener type and spacing of their fire test. The number of screws per sheet then depends on your framing spacing, so count from your layout or ask your supplier.
In Excel or Google Sheets
If the drywall square feet for the walls is in A2 and the waste percent is in B2, the 4x8 sheets are:
=ROUNDUP(A2*(1+B2/100)/32, 0)
Microsoft's help page says ROUNDUP "Rounds a number up, away from 0 (zero)", and Google's says it rounds "always rounding up to the next valid increment". Use 40 or 48 in place of 32 for 4x10 or 4x12 sheets, and work the ceiling out in its own cell.
Questions and answers
How many sheets of drywall do I need for a 12 x 12 room?
With 8 ft walls, one door and one window, the walls are 351 sq ft and the ceiling 144 sq ft. With 10% waste that is 13 sheets of 4x8 for the walls and 5 for the ceiling, 18 in all, or 13 sheets of 4x12.
How many square feet are in a sheet of drywall?
Length times width: a 4x8 sheet is 32 sq ft, a 4x10 is 40 sq ft and a 4x12 is 48 sq ft.
Should I subtract doors and windows?
The calculator does, using the sizes you set. If you leave them in, the extra sheets act as spare for cuts around openings, which some people prefer on small jobs.
How much waste should I allow for drywall?
There is no single rule. USG's own estimator leaves waste out. 10% is a common starting point; use more for rooms with many corners, angles or cut-outs.
Does the calculator work in meters?
Yes. Choose Meters and type sizes in meters and centimeters. Pick Other size and type the size of the sheet you will buy; the result is still a count of whole sheets.
Sources
Checked on 9 October 2026. If a rule has changed, please tell us.
- USG: Sheetrock Brand UltraLight Tough Panels product page (panel sizes)
- USG: Sheetrock Wallboard Estimator (waste not included)
- USG: Sheetrock Brand Paper Joint Tape submittal sheet J1736 (tape coverage and roll sizes)
- USG FAQ: joint compound coverage for joint finishing
- USG FAQ: fastening gypsum panels to walls and ceilings
- Microsoft Support: ROUNDUP function
- Google Docs Editors Help: ROUNDUP