How to use
- Choose a room or a known area. For a room, enter length, width, and wall height. Eight feet is only a starting height.
- Check the ceiling if you will hang drywall there. It adds length times width and does not get the door deduction.
- Enter how many doors and windows, and the square feet of each. A 3 foot by 7 foot door is 21 square feet, which is why 21 is the starting door size. Measure yours.
- Pick a 4×8 or 4×12 sheet, or type a custom sheet area. Set waste. Press Calculate.
How it's calculated
Ceiling = length × width, if included
Net = gross − openings
Sheets = ceiling( net × (1 + waste ÷ 100) ÷ sheet area )
The wall formula is the perimeter times the height, which counts all four walls and ignores closets unless you add them. Openings are subtracted once. Waste is applied after that, and the sheet count rounds up. A 4×8 sheet is 4 × 8 = 32 square feet by arithmetic, not by a brand’s coverage claim.
Paint for the finished wall is a different unit. Gallons are on the paint calculator. If you need the floor area of the same room for another trade, SqftKit totals square feet without pretending to count drywall sheets.
Worked example
A 12 by 10 foot room with 8 foot walls has a perimeter of 44 feet and a wall area of 352 square feet. One 21 square foot door and one 15 square foot window leave 316 square feet. Ten percent waste makes 347.6 square feet. Divided by 32, that is 10.86, which rounds up to 11 sheets of 4×8. The same net area on 4×12 sheets of 48 square feet is 8 sheets, because 347.6 ÷ 48 = 7.24, and that rounds up to 8.
Assumptions and sources
Sheet areas are the product of the nominal 4 foot width and the 8 or 12 foot length. Real panels can be a hair short of those nominal sizes; if that matters for a layout, type a custom sheet area you measured. The door default of 21 square feet is 3 × 7, a common slab, not a rule. Waste covers offcuts and damage and is yours to change. The tool does not lay out joints or count screws.
FAQ
How many square feet is a sheet of drywall?
A 4 by 8 foot sheet is 32 square feet. A 4 by 12 foot sheet is 48 square feet.
Should I subtract windows?
Yes, if you will not cover them. Enter the count and the area of each. Tiny openings are optional; a window is large enough to matter.
Does the ceiling use the same sheets?
Yes. Check the ceiling box and the ceiling area is added before the sheet count. Doors are not subtracted from the ceiling.
Why round up?
You cannot buy a fraction of a sheet. The last partial sheet is a whole sheet in the order.