Drywall is bought by the sheet but finished by the foot: every seam needs tape and several coats of joint compound, and every sheet needs a few dozen screws. This calculator measures a room’s walls and ceiling, subtracts doors and windows, adds a waste allowance and converts the result into sheets of the size you plan to hang. It also estimates the finishing materials, so you can bring everything home in one trip.
How to use the drywall calculator
- Pick US or Metric units.
- Choose Room size and enter length, width and wall height, or choose Known area if you have already measured the surfaces.
- Leave Include the ceiling ticked if the ceiling is being covered too.
- Enter the number of doors and windows and the area of each opening.
- Choose a sheet size: 4 × 8, 4 × 10 or 4 × 12 ft (or 1200 mm wide metric board).
- Set the waste allowance and, if you like, the compound rate and price per sheet.
Drywall formulas
Finishing materials are scaled from the net board area using typical rates: about 1 gallon of compound and 37 feet of paper tape per 100 ft², and about one screw per square foot of board hung.
Worked example: a 14 × 12 ft bedroom
Walls: 2 × (14 + 12) × 8 = 416 ft². Ceiling: 14 × 12 = 168 ft². Total 584 ft².
Openings: one 21 ft² door and two 15 ft² windows = 51 ft², leaving 533 ft².
With 10% waste: 533 × 1.1 = 586.3 ft² ÷ 32 ft² = 18.3 → 19 sheets of 4 × 8 (or 13 sheets of 4 × 12).
Compound: 5.3 gal (two 4.5-gal pails). Tape: about 198 ft. Screws: about 650.
Choosing the right board
| Board | Typical use |
|---|---|
| 1/2 in regular | Most interior walls |
| 1/2 in sag-resistant ceiling board | Ceilings, especially with framing 24 in on center |
| 5/8 in Type X (fire-rated) | Garage walls and ceilings next to living space, fire-rated assemblies |
| Moisture- and mold-resistant | Bathrooms, laundry rooms, basements (not as a tile backer in showers) |
| 1/4 or 3/8 in flexible | Curved walls and resurfacing old plaster |
Building codes require specific board in some places. The International Residential Code, for example, calls for gypsum board on the garage side of walls shared with the house and 5/8-inch Type X on garage ceilings with living space above. Check with your building department before you buy.
Hanging tips that save material
- Hang ceilings first, then walls, so the wall sheets support the ceiling edges.
- Run sheets horizontally on walls up to about 8 ft 1 in tall: two 4-ft-wide rows cover the height with a single horizontal seam at a comfortable working height.
- Use the longest sheet you can handle. Fewer butt joints mean less taping and a flatter finish.
- Don’t piece around openings. Hang over windows and doors and cut out the opening with a router or saw; small offcuts rarely save money and create extra joints.
- Stagger butt joints between rows so they do not line up on the same stud.
Finishing materials
Paper tape is standard for flat joints and inside corners; mesh tape is quicker for patches but needs setting-type compound. Outside corners take metal or paper-faced corner bead, which this calculator does not count, so measure each outside corner separately. Plan on a coarse-thread 1-1/4 in screw for 1/2-inch board on wood studs and a fine-thread screw for steel studs.
After the board is finished and primed, the paint calculator estimates the gallons for the same walls. If you are opening up exterior walls, the insulation calculator gives recommended R-values before the drywall goes on, and for odd-shaped rooms the square footage calculator helps total the areas first.
Frequently asked questions
How many sheets of drywall do I need for a 12 × 12 room?
With 8-foot walls the walls total 384 ft² and the ceiling 144 ft². Subtracting a door and two average windows leaves about 477 ft². Adding 10% for waste and dividing by 32 ft² per 4 × 8 sheet gives 17 sheets, or 11 sheets of 4 × 12.
Is it better to use 4 × 8 or 4 × 12 drywall?
Longer sheets cover more area per seam, so a wall finished with 4 × 12 board has fewer butt joints to tape and sand. They are heavy (a 1/2-inch 4 × 12 sheet weighs roughly 55–80 lb depending on the type) and hard to get up stairs, so many DIYers stick with 4 × 8 for walls and use longer sheets only on long walls or ceilings with help.
How much joint compound do I need per sheet?
A common rule of thumb is about 1 gallon of ready-mixed compound per 100 ft² of board for taping plus two finish coats, or roughly one-third of a gallon per 4 × 8 sheet. A 4.5-gallon pail finishes about 450 ft². Heavy texture or a level 5 skim coat uses noticeably more.
Should I subtract windows and doors from a drywall estimate?
Subtract doors and large windows, because they can remove 50 ft² or more from a room. Many hangers run full sheets across small windows and cut the opening out afterward, so the cutout becomes waste; that is one reason a 10–15% allowance is normal.
How many screws does a sheet of drywall take?
On studs 16 inches apart, a 4 × 8 sheet hung on a wall takes about 28–32 screws, roughly one per square foot. Ceilings are usually fastened more closely, so plan a few more there.