Combining walls and ceiling
A drywall estimate covers both the walls and, in most rooms, the ceiling. Wall area is the room perimeter times the ceiling height, which for a rectangular room is 2 times (length plus width) times height. Ceiling area is simply length times width. Adding the two gives the total surface to be boarded. Leaving door and window openings in the total is common practice because the offcuts rarely go far enough to reuse, so the openings become a built-in safety margin.
How you handle the ceiling changes both the sheet count and the labor. Hanging drywall overhead is the hardest part of any drywall job because the sheets must be held against gravity while they are fastened, so many people rent a drywall lift or work in pairs for ceilings. If the ceiling is skipped in favor of a suspended grid, drop it from your sheet total and count only the walls. Remember too that wall height rarely matches sheet dimensions perfectly: an 8-foot wall is covered by two 4-foot-wide sheets hung horizontally with no waste, while a 9-foot wall forces an extra rip strip along the top, adding both material and seams to finish.
Sheet size trade-offs
Drywall comes in 4-foot-wide sheets of varying length, and the size you choose changes both the seam count and the labor. A 4 by 8 sheet covers 32 square feet and is manageable for one person; a 4 by 12 sheet covers 48 square feet, spans a longer wall in one piece, and leaves fewer joints to tape and finish, but it is heavy and awkward to handle in tight spaces. Fewer seams mean a smoother finished wall and less mudding, so pros favor longer sheets on open walls and drop to shorter sheets in cramped rooms and stairwells.
Mud, tape, screws, and corner bead
The board is only the start of the material list. As rough working figures, plan on roughly one pound of drywall screws per 100 to 150 square feet of board, about 40 linear feet of joint tape per 100 square feet, and a 4.5-gallon bucket of premixed joint compound for every 400 to 500 square feet across the taping and finishing coats. Every outside corner needs corner bead measured by the linear foot. These are estimates that vary with technique and coat count, so buy a margin above the calculation.
Bear in mind that compound usage climbs with the level of finish you want. A garage or closet may need only tape and two coats over the seams, while a smooth wall destined for glossy paint or raking light can demand a skim coat over the entire surface, which uses dramatically more mud than seam-and-screw finishing alone. Estimate compound for the finish level the room actually requires, not just the seam length, and keep in mind that lightweight all-purpose compound is easier to sand while setting-type compound sets faster and is stronger for the first taping coat.
- Screws: about 1 lb per 100 to 150 sq ft of drywall.
- Tape: roughly 40 linear ft per 100 sq ft of board.
- Joint compound: about one 4.5-gallon bucket per 400 to 500 sq ft.
- Corner bead: measured and ordered by the linear foot.
Fire-rated and specialty board
Not all drywall is interchangeable. Type X fire-rated board, usually 5/8 inch thick, is required by code in garages, on walls shared with living space, and in many ceilings; it weighs more and costs more than standard 1/2 inch board. Moisture-resistant and mold-resistant panels belong in bathrooms and other damp areas, and cement board is the right base under tile in wet zones. Identify which rooms need which board before you total your order, because mixing the wrong type into a rated assembly can fail inspection.