Calculators · Drywall Calculator
Walls & FinishesDrywall Calculator
Add your walls and ceilings, choose whether to subtract doors and windows, and get the number of drywall sheets, plus tape, screws and compound.
Drywall sheets to buy
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How to calculate how much drywall you need
Drywall is bought in sheets, so you work out the area to cover and divide it by the area of one sheet. Measure each wall and each ceiling, add them up, and round the result up to a whole sheet:
| Step | Formula |
|---|---|
| Wall | length × height |
| Ceiling | length × width |
| Door or window | width × height |
| Area to cover | walls + ceilings (− openings, if you subtract them) |
| Area to order | area to cover × (1 + waste ÷ 100) |
| Sheets to buy | area to order ÷ area of one sheet, rounded up |
If you only know the size of the room, the four walls together are the distance around the room times
the wall height. Walls that are the same size can share one row: type the number of identical walls in
the last box. Each measurement accepts feet and inches written as 9'6", and you can switch
any box to inches, yards or meters.
Should you subtract doors and windows?
It depends on whom you ask. The USG installation guide for SHEETROCK panels says to subtract the square footage of large openings such as doorways and picture windows, and not to bother with small openings such as electrical boxes and pipe fittings. The CertainTeed drywall calculator takes the opposite approach and tells you not to subtract for openings like doors, windows or outlets. Both are manufacturer guidance, so the calculator has a switch. List your doors and windows and choose to subtract them, or choose not to subtract and the calculator still shows what they would have taken off.
Example: a 12 by 14 foot room with an 8 foot ceiling
A room is 14 ft long and 12 ft wide with 8 ft walls, and you will board the four walls and the ceiling with 4 by 8 foot sheets. It has one door of 3 ft by 7 ft and one window of 3 ft by 4 ft. This is what the calculator does with those numbers:
| Step | Operation | Result |
|---|---|---|
| Long walls | 2 × 14 × 8 | 224 sq ft |
| Short walls | 2 × 12 × 8 | 192 sq ft |
| All four walls | 224 + 192 | 416 sq ft |
| Ceiling | 14 × 12 | 168 sq ft |
| Walls and ceiling | 416 + 168 | 584 sq ft |
| Door and window | 3 × 7 + 3 × 4 | − 33 sq ft |
| Area to cover, openings subtracted | 584 − 33 | 551 sq ft |
| Sheets, openings subtracted | 551 ÷ 32 = 17.22 | 18 sheets |
| Sheets, openings not subtracted | 584 ÷ 32 = 18.25 | 19 sheets |
The same room needs 18 sheets if you subtract the door and the window and 19 if you do not. That is the whole difference between the two manufacturer approaches for this room.
Sheets needed by area and sheet size
If you already know the total area to cover, this table shows the sheets needed in each size, rounded up and without waste.
| Area to cover | 4×8 (32 sq ft) | 4×9 (36 sq ft) | 4×10 (40 sq ft) | 4×12 (48 sq ft) |
|---|---|---|---|---|
| 200 sq ft | 7 | 6 | 5 | 5 |
| 400 sq ft | 13 | 12 | 10 | 9 |
| 600 sq ft | 19 | 17 | 15 | 13 |
| 800 sq ft | 25 | 23 | 20 | 17 |
| 1,000 sq ft | 32 | 28 | 25 | 21 |
| 1,200 sq ft | 38 | 34 | 30 | 25 |
Drywall sheet sizes
The Gypsum Association lists gypsum panels that are 48 inches wide in lengths of 8, 9, 10, 12, 14 and 16 feet, and also a 54 inch wide panel in 12 foot lengths. Its table shows 1/2 inch and 5/8 inch as the thicknesses for any interior use and some protected exterior uses. Not every type is made in every size, so check what your supplier stocks. The area of a sheet is its width in feet times its length. The USG coverage table agrees for 4 by 8, 4 by 10 and 4 by 12 foot sheets, where ten sheets cover 320, 400 and 480 square feet. Checked in October 2026.
Tape, screws and joint compound
USG gives the quantities of fasteners, tape and compound for a given area of SHEETROCK panels. They scale in a straight line with the area, so the calculator multiplies the area to cover by these figures per 1,000 square feet:
| Material (USG) | Per 1,000 sq ft |
|---|---|
| Joint tape | 370 ft |
| Screws (Type W, 12 in apart on ceilings, 16 in on walls) | 2.7 lb |
| Nails (7 in apart on ceilings, 8 in on walls) | 5.3 lb |
| All purpose ready mixed joint compound | 138 lb |
| Lightweight all purpose ready mixed compound (PLUS 3) | 9.4 gal |
| First coat compound | 2.9 gal |
For the 551 square feet of the example room that is about 204 feet of tape, 1.5 pounds of screws and 76 pounds of all purpose compound. USG describes the compound figures as approximate for flat joints, inside corners and outside corners with metal corner bead in a typical room, and warns that coverage can vary widely with the surface, the tools and the method. Treat them as a starting point.
Sources: USG, SHEETROCK Brand Gypsum Panels installation and finish guide (2003), Gypsum Association, GA-223-04, Gypsum Panel Products: Types, Uses, Sizes, and Standards, USG Sheetrock wallboard estimator and CertainTeed drywall calculator. The USG guide dates from 2003 and we found its copy on a third party site, so confirm the figures with the current installation instructions of the brand you buy. Checked in October 2026.
How much waste to add
Leave the waste box empty to see the exact count. We could not find a waste percentage published by a drywall manufacturer. The USG Sheetrock wallboard estimator says its estimate does not include an allowance for waste, and CertainTeed says its calculator does not include allowances for potential waste. Real rooms have cut pieces and offcuts, so ask your supplier or installer which figure they use for your job and type it in.
What this calculator does not do
It gives the number of sheets and, if you choose, the tape, fasteners and joint compound. It does not give prices and it does not count corner bead, adhesive, texture, primer, stud framing or insulation. It does not choose the thickness or the type of board for you, because that depends on the framing, the room and your local code.
Frequently asked questions
How do you calculate how many sheets of drywall you need?
Find the area of every wall (length × height) and every ceiling (length × width), add them together, and divide by the area of one sheet. A 4 by 8 foot sheet covers 32 square feet. Round up, because you cannot buy part of a sheet. For a 12 by 14 foot room with 8 foot walls, the walls are 416 square feet and the ceiling is 168 square feet. That is 584 square feet, or 18.25 sheets, so you buy 19 sheets of 4 by 8.
How many sheets of drywall do I need for a 12x12 room?
It depends on the wall height. With 8 foot walls and a ceiling, the four walls are 4 × 12 × 8 = 384 square feet and the ceiling is 12 × 12 = 144 square feet. The total is 528 square feet, which is 16.5 sheets, so 17 sheets of 4 by 8 before waste and before any openings. Type your own room into the calculator to include doors, windows and waste.
Do you subtract windows and doors when you calculate drywall?
The two manufacturers we checked disagree. The USG installation guide says to subtract large openings such as doorways and picture windows, and not to bother with small ones such as electrical boxes. The CertainTeed drywall calculator says not to subtract for openings like doors, windows or outlets. This calculator lets you choose.
How much waste should I add to a drywall order?
We could not find a waste percentage published by a drywall manufacturer. The USG online estimator says its estimate does not include an allowance for waste, and CertainTeed says the same about its calculator. Ask your supplier or installer which figure they use for your job, then type it in the waste box. Leave the box empty to see the exact count.
What size drywall sheets are there?
The Gypsum Association lists gypsum panels 48 inches (4 feet) wide in lengths of 8, 9, 10, 12, 14 and 16 feet, and a 54 inch wide panel in 12 foot lengths. The calculator has 4 by 8 (32 square feet), 4 by 9 (36), 4 by 10 (40) and 4 by 12 (48), and a box for any other size. It also shows how many sheets the same area needs in each of those four sizes.
How much joint tape, screws and joint compound do I need?
USG publishes quantities per 1,000 square feet of panels: 370 feet of joint tape, 2.7 pounds of screws and 138 pounds of ready mixed all purpose joint compound. The calculator scales those figures to your area. USG says the compound figures are approximate for a typical room and can vary widely with the surface, the tools and the method. The figures do not include waste.
How thick should the drywall be and how far apart can the framing be?
Thickness does not change the number of sheets, but it matters for the job. The Gypsum Association lists 1/2 inch and 5/8 inch panels for any interior use and some protected exterior uses. In its table for single layer application to wood framing, USG allows 1/2 and 5/8 inch panels on walls at up to 24 inches on center. On ceilings it allows 24 inches when the panels run perpendicular to the framing and 16 inches when they run parallel. For 1/2 inch ceiling panels, the same table says the maximum is 16 inches even when perpendicular if a water-based texture is to be applied, and it does not recommend running them parallel to the framing with that kind of texture. Fire rated assemblies and local codes can require something different, so check with your building department.
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