Drywall Calculator

How Many Drywall Sheets a Room Needs

Drywall is counted by area. Add the wall area to the ceiling area, divide by the area of one sheet, round up, then add 10 percent for offcuts, damaged boards and the pieces that end up too short to use anywhere.

A worked example

A bedroom 12 feet by 16 feet with an 8 foot ceiling. The perimeter is 2 x (12 + 16), which is 56 feet, so the wall area is 56 x 8, or 448 square feet. The ceiling is 12 x 16, or 192 square feet. Total board area is 640 square feet. Add 10 percent and that is 704 square feet. In 4 ft by 8 ft sheets, 704 divided by 32 is exactly 22 sheets. In 4 ft by 12 ft sheets, 704 divided by 48 is 14.67, so 15 sheets.

Do not deduct small openings. A standard door is about 21 square feet and a window about 15, but the board around them is cut from full sheets and most of the cutout is waste. Deduct only where an opening is larger than about 30 square feet, such as a wide cased opening or a garage door.

Sheet Sizes and Why 12 Foot Board Wins

Drywall comes 4 feet wide in 8, 9, 10, 12 and sometimes 14 foot lengths. The 8 foot sheet is the only one most people can carry alone and the only one that fits in a pickup bed, which is why it dominates DIY work. On a professional job it is the wrong choice almost everywhere.

The reason is joints. A 16 foot wall with an 8 foot ceiling, boarded horizontally with 8 foot sheets, has one butt joint in the middle of each row. With 12 foot sheets and a 4 foot filler, the butt joint moves to a quarter point and there is one instead of one per row per side. Fewer joints means less tape, less compound, less sanding and, most importantly, fewer butt joints, which are the joints that show. Tapered edges hide themselves in the factory bevel, but butt joints have no recess and have to be feathered wide to disappear.

Hang the board perpendicular to the framing wherever possible. On walls that means horizontally, which puts the tapered seam at about 4 feet, a comfortable working height, and crosses more studs for stiffness.

Board Thickness and Type

• 1/2 inch regular: the default for walls and ceilings in a house with framing at 16 inches on center. Standard sheets weigh about 1.6 pounds per square foot, so a 4 x 8 is roughly 51 pounds.
• 5/8 inch type X: fire rated board. Required by code on the wall and ceiling between an attached garage and the living space, in many multi family separation assemblies, and commonly used on ceilings with framing at 24 inches on center because it sags less. It also cuts sound transmission noticeably.
• Moisture resistant board: green board and the newer paperless boards go in bathrooms, laundry rooms and behind sinks. Neither is a tile backer. Anything inside a shower or tub surround needs cement board or a proper waterproof panel system.
• Lightweight 1/2 inch: roughly 25 percent lighter than standard and easier to handle overhead, but it is not rated for 24 inch framing on ceilings unless the manufacturer says so.
• Abuse and impact resistant: heavier facing and a reinforced core, used in hallways, garages and rental properties.

Joint Compound, Tape and Screws

Allow about 0.053 gallons of joint compound per square foot of board for a full three coat finish, which works out to roughly 1 gallon for every 20 square feet. That is a generous allowance covering tape coat, fill coat, finish coat and the material lost to sanding. Experienced tapers using setting compound for the first coats will use less. The 640 square foot bedroom above needs roughly 32 gallons at that rate, which is about seven of the 4.5 gallon buckets, so buy in stages rather than all at once.

Tape runs about 0.5 linear feet per square foot of board, so 640 square feet of board takes about 320 feet of tape. Buy the 500 foot roll. Paper tape is stronger and is the right choice for inside corners; mesh tape is faster on flat seams but should be coated with a setting compound rather than a ready mix for the first pass.

Count screws per sheet rather than by weight. The old rule of a pound per 1,000 square feet is far too low to be useful. Use about 32 screws per 4 x 8 sheet on walls, with fasteners at 16 inches on center in the field and 8 inches at the edges. Ceilings need more, closer to 36 to 40 per sheet, at 12 inches on center in the field. Use 1 1/4 inch screws for 1/2 inch board and 1 5/8 inch for 5/8 inch board.

Levels of Finish

The finish levels are an industry standard, and specifying one avoids arguments about what a finished wall means.

• Level 0: board hung, nothing taped. Temporary construction only.
• Level 1: tape set in compound at all joints. Used above ceilings and in concealed plenum spaces.
• Level 2: one coat over tape and fasteners. Used in garages, under tile, and in warehouses.
• Level 3: two coats. Suitable under heavy texture, not under flat or eggshell paint.
• Level 4: three coats, sanded smooth. The normal residential standard for flat paint and light texture.
• Level 5: level 4 plus a thin skim coat over the whole surface. Needed under gloss paint, under strong side lighting, and on any wall where the light rakes across it.

Sheets by Room Size

Counts assume no deductions for doors or windows, which is the safe way to order. Adjust the wall area for ceilings higher or lower than 8 feet by multiplying the perimeter by the real height.