How to use the drywall calculator
- Add a row for each wall or ceiling. Pick the type, then enter the length and the height (for a wall) or width (for a ceiling), in feet.
- Enter the area of doors and windows on that surface in square feet so it can be deducted.
- Choose a sheet size (4x8, 4x10 or 4x12) and keep or change the 10% waste allowance.
- Read the sheets to buy, rounded up. The rough screw and joint compound lines are estimates based on per-sheet factors you can edit under More options.
Formula
Surface area = length x height (wall) or length x width (ceiling)
Net area = surface area - openings
Sheets = total net area x (1 + waste percent) / sheet area, rounded up
Sheet area: 4x8 = 32 sq ft, 4x10 = 40 sq ft, 4x12 = 48 sq ft
Estimate: screws = sheets x screws per sheet; compound = sheets x gallons per sheet
The screw and compound lines are rough estimates. They multiply the number of sheets by a factor that you can change, so treat them as a shopping starting point.
Worked example: a small room with a long wall, a short wall and a ceiling
A 12 ft by 8 ft wall with a 20 sq ft door is 96 - 20 = 76 sq ft. A 10 ft by 8 ft wall with a 15 sq ft window is 80 - 15 = 65 sq ft. A 12 ft by 10 ft ceiling is 120 sq ft.
The total is 76 + 65 + 120 = 261 sq ft. With a 10% waste allowance that is 287.1 sq ft.
With 4x8 sheets (32 sq ft each) you need 287.1 / 32 = 8.97, so 9 sheets. With 4x10 sheets it is 7.18, so 8 sheets, and with 4x12 sheets it is 5.98, so 6 sheets.
Rough estimates at 32 screws and 0.3 gallons of compound per sheet: about 288 screws and 2.7 gallons of joint compound for 9 sheets.
Choosing a sheet size
Longer sheets mean fewer seams to tape and finish, and a tall wall can sometimes be covered with one piece. They are also heavier and harder to carry through doors and up stairs. The calculator shows all three sheet sizes from the same area, so you can see how each one affects the count and decide based on your space and your helpers.
Openings and waste
Deducting doors and windows saves board, but it also removes material you may need for cut-outs. Many installers deduct only large openings, and the waste allowance covers the rest. Enter whichever approach you prefer. You can leave the openings box blank for none and rely on the allowance alone.
Ceilings and walls are listed separately so you can see the split. Hanging the ceiling first is common, but that is a sequencing choice that does not change the quantity.
About the screw and compound estimates
Fastener count depends on spacing rules, framing layout and the product. Compound depends on the finish level, the number of coats and how much sanding and waste you accept. For those reasons the tool shows them as rough estimates from simple per-sheet factors, and it never presents them as exact. Tape, corner bead, primer and paint are separate. Once the walls are up, the paint calculator can turn the same measurements into gallons.
Assumptions and limits
- Sheets are 4 ft wide and the lengths shown. Thickness and board type are not modeled.
- Screws per sheet (32) and joint compound per sheet (0.3 gallon) are rough estimates and editable. The defaults are sized for a 4x8 sheet, so raise them for larger sheets.
- Openings are the square feet you enter. The tool does not guess door or window sizes.
- Each surface is a rectangle. Gables, soffits, stairwells and angled ceilings should be split into rectangles.
- This is a planning estimate. Confirm quantities with your supplier and follow local codes for fire, moisture and fastening requirements.
Frequently asked questions
How many sheets of drywall do I need for a 12 by 12 room?
Four 8 ft walls total 384 sq ft and the ceiling adds 144, so 528 sq ft before openings and waste. With 10 percent waste that is about 18.2 sheets of 4x8, so 19. Enter your own sizes for a closer figure.
Should I subtract windows and doors?
You can. It lowers the count, but pieces cut out of openings are often reused elsewhere, so some builders deduct only large openings. Use the openings box for whatever approach you prefer.
How much extra drywall should I buy?
It depends on the layout and your skill. This tool starts at 10 percent, which is only a starting point, and you can set any value from 0 to 100.
How many screws are in a typical box?
Box sizes vary by product, so this calculator shows a rough total number of screws and leaves the conversion to boxes to you. Check the label of the box you plan to buy.
Does the calculator include tape and corner bead?
No. Tape, corner bead and primer are separate items and depend on the number of seams and corners. Count linear feet of corners and seams from your plan.