Drywall
Room in, buy list out — sheets with waste, and the screws, mud and tape that never make it onto the list.
Your buy list
0
sheets of 4 × 8- Wall area
- —
- Ceiling area
- —
- Screws
- —
- Joint compound
- —
- Tape
- —
Openings deducted; waste added after.
Counting sheets
Wall area is the perimeter times the ceiling height — twice the length plus twice the width, multiplied by how tall the room is. A standard door takes 21 square feet off that and a window about 12. If the ceiling is going on too, add the floor area again. Divide the total by the sheet size, add waste, and round up: sheets are not sold in halves.
Waste on drywall is not the same waste as on flooring. Most of it is offcuts you cannot reuse — the strip above a door, the corner that broke carrying it upstairs, the sheet measured against the wrong stud. Ten percent covers a square room. Add more for a room full of angles, soffits or a stairwell.
The materials nobody lists
Hanging is a day; finishing is three. Every sheet takes about 32 screws at 12 inches on centre — call it a pound of screws for every nine or ten sheets. A 4.5 gallon box of all-purpose compound covers roughly 475 square feet of board through tape and two coats, and paper tape runs about 37 feet per 100 square feet. Buy all of it at once; running out of mud on a Sunday afternoon costs more than the box did.
Then it gets painted
New board drinks paint. Prime it with a dedicated drywall primer — the paper and the dried compound absorb at completely different rates, and colour over unprimed board flashes at every joint. Take the same room dimensions to the paint calculator for the gallons, and count the primer as a separate coat.
On the counter
The assumptions this calculator ships with — every one is adjustable in the form.
- Sheet size
- 4 × 8 = 32 sq ft by default; 4 × 10 and 4 × 12 in the dropdown
- Waste
- 10 % — cut-offs, damaged corners and the piece that measures wrong
- Screws
- 32 per sheet at 12 in on centre; about 300 #6 screws to the pound
- Compound and tape
- One 4.5 gal box per 475 sq ft; 37 ft of tape per 100 sq ft
Questions from the aisle
How many sheets of drywall for a 12x12 room?
Walls are 384 square feet gross, about 339 after a door and two windows come off; add a 144 square foot ceiling and it is 483. At 10% waste on 4×8 sheets that is 17 sheets for walls and ceiling — plus two pounds of screws, two boxes of compound and 200 feet of tape. Walls only, it is 12 sheets.
4x8, 4x10 or 4x12 sheets?
Longer sheets mean fewer butt joints, which are the hardest joints to hide. On an 8 foot wall, 4×12 sheets hung horizontally can span a whole wall with one seam at 4 feet. They are also heavy and awkward — 4×8 is what fits in most vehicles and up most staircases.
How much joint compound do I need?
About one 4.5 gallon box per 475 square feet of board for a taped, three-coat finish. Skim-coating for a level 5 finish roughly doubles it, and hot mud used for the first coat comes in bags you mix yourself.
Do I deduct doors and windows?
Deduct the openings, but do not deduct the waste. The board cut out over a door usually cannot be used anywhere else, so this calculator subtracts openings from the area and then adds the waste percentage back on top.
The reasoning behind this one
How to measure a room
Where the assumptions above come from, what changes them, and the mistakes that cost a second trip. Free to read, no account needed.