Drywall calculator
Enter the size of the room and of the sheets to see how many sheets of drywall you need, with extra for cuts. Take away doors and windows, and add the ceiling if it is covered too.
This answer is for the example values in the boxes above. A room 12 by 10 ft with 8 ft walls and the ceiling, sheets 4 by 8 ft, 10% extra. Change the boxes to see your own answer.
The walls are the perimeter times the height. The count is by area: the extra is for cuts, seams and mistakes.
How it works
The walls are the distance around the room times the height. If the ceiling is covered too, its area is the length times the width. The calculator takes away the doors and windows you give it, adds the extra, divides by the area of one sheet and rounds up to whole sheets.
A worked example
A room 12 feet long and 10 wide with 8 foot walls has a perimeter of 44 feet and 352 square feet of walls. The ceiling adds 120. A door of 3 by 7 feet is 21 square feet and a window of 3 by 5 is 15, so together they take away 36, and 436 square feet are left.
One sheet of 4 by 8 feet covers 32 square feet, and 436 divided by 32 is 13.625, so 14 sheets cover the room. With 10 percent extra the area is 479.6 square feet, which is 14.99 sheets, and you buy 15.
Without the ceiling the walls come to 316 square feet. That is 10 sheets, or 11 with the extra. Sheets of 4 by 12 feet cover the room and its ceiling in 10.
The size of the sheets
The calculator takes the width and the length of the sheet from you and starts with 4 by 8 feet. Makers list several sizes. One data sheet for a 5/8 inch Type X board gives widths of 4 feet, 54 inches and 60 inches and lengths from 8 to 14 feet. Another gives a width of 4 feet and lengths from 8 to 12 feet.
What it leaves out
The count is by area. It does not lay the sheets out on the wall, so the direction of the sheets, the seams and the waste of a real layout are what the extra is for. It does not count screws, tape or joint compound.
Sources
- Georgia-Pacific, ToughRock Fireguard X gypsum board, product data, read on 2026-11-02.
- American Gypsum, M-BLOC Type X gypsum board, product data, read on 2026-11-02.
Questions
How many sheets of drywall do I need for a room?
Add the area of the walls and the ceiling, subtract doors and windows, add some extra, and divide by the area of one sheet. A room of 12 by 10 feet with 8 foot walls and a ceiling, less 36 square feet of door and window, is 436 square feet. That is 14 sheets of 4 by 8 feet, or 15 with 10% extra.
How many square feet are in a sheet of drywall?
A sheet of 4 by 8 feet covers 32 square feet, and a sheet of 4 by 12 feet covers 48. Multiply the width by the length of your own sheet.
How do I find the area of the walls?
Multiply the distance around the room by the wall height. A room of 12 by 10 feet has a perimeter of 44 feet, so walls 8 feet high are 352 square feet.
How much extra should I add?
The calculator starts at 10%, which is its own starting value and not a rule. Seams, cuts and mistakes use part of every sheet, and a job with many cuts may need more.
What size are drywall sheets?
Makers list several. Two data sheets for 5/8 inch Type X board give widths of 4 feet, one of them also 54 and 60 inches, and lengths from 8 feet up to 12 or 14. Type the size of the sheets you will buy.
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