Drywall is bought by the sheet and used by the square foot, and the sheet size you choose changes both the count and the amount of finishing work waiting for you. This drywall calculator handles walls and ceiling together and shows the result in sheets.
Sheet size is the decision, not the quantity
A 16 by 12 foot room with 8 foot ceilings has 640 square feet of wall and ceiling before deductions. Which sheet you specify changes the order substantially:
- 4 by 8 sheets cover 32 square feet each. This room takes 21 of them.
- 4 by 12 sheets cover 48 square feet each. The same room takes 14.
Seven fewer sheets is not the real prize. Every seam gets taped, filled, sanded and eventually lit by a lamp at a shallow angle, and longer sheets mean fewer of them. Twelve foot board on a twelve foot wall means no butt joints in that wall at all, and butt joints are the ones that show. The Gypsum Association’s GA-216 requires the end joints you do create to be staggered between alternate courses.
Weigh that against handling. A 4 by 12 half-inch sheet runs close to 80 pounds and is a genuine two-person lift. It will not go up a tight stairwell or round a turn in a hallway, and it costs more per sheet than a 4 by 8. Fewer joints is the right call when the access allows it and the wrong one when it does not.
The ceiling is half the job again
Walls alone in this room are 448 square feet, about 14 standard sheets. Add the ceiling and it becomes 640 square feet and 21 sheets, so the ceiling is a full 50% on top of the walls.
It is also the harder half. Ceiling board is hung first, wants a lift or a second pair of hands, and on a ceiling most installers step up to 5/8 inch board for sag resistance, which is heavier again.
Openings, and why the deduction is planning only
This page takes doors off at 21 square feet and windows at 15, which is right for working out what to order. It is not how the board goes up.
Most hangers sheet straight over an opening and cut it out afterwards with a router against the frame, because a cut made in place is faster and straighter than one measured on the floor. The offcut is waste by then, and the allowance above is what covers it.
Order the finishing materials with it
Board is only the first of four purchases, and the others scale off the same measurements. Budget roughly 350 feet of tape and 10 gallons of joint compound per 1,000 square feet of board for three coats, plus 2.7 pounds of screws per 1,000 square feet.
Once the walls are finished, the paint calculator works out the coats going over them, and bare board drinks more paint than the label suggests.
Drywall calculator FAQ
About 21 standard 4 by 8 sheets for walls and ceiling with an 8 foot ceiling, covering 640 square feet before deductions. Using 4 by 12 sheets instead brings it down to 14 sheets and far fewer joints.
Use 4 by 12 where access allows. Longer sheets mean fewer taped joints, and on a 12 foot wall no butt joints at all. They weigh close to 80 pounds each, need two people, and will not negotiate a tight stairwell.
At around $16 for a standard 4 by 8 sheet, a 12 by 16 room with a ceiling runs about $336 in board alone. Add tape, joint compound, screws and corner bead, which together add meaningfully to the total.
For ordering, yes, at roughly 21 square feet per door and 15 per window. On site most installers hang straight over openings and cut them out afterwards, so that material becomes waste and the allowance covers it.