How the calculator works it out
It adds up the wall area of every room, takes off doors and windows, and keeps ceilings separate because they get more screws and are often a different board. Each total gets the waste allowance and is divided by the sheet size. Mud and tape are worked out from the finished board area using manufacturer rates.
Wall area = 2 × (length + width) × height − doors × 21 − windows × 15
Sheets = area × (1 + waste %) ÷ sheet area (32, 40 or 48 sq ft), rounded up
Joint compound = area ÷ 1,000 × 9 gallons · Tape = area ÷ 1,000 × 350 ft
Screws = sheets × screws per sheet
Worked example: a 12 × 14 ft room with a ceiling
Walls: 2 × 26 × 8 = 416 square feet, less 21 for the door and 30 for two windows, is 365 square feet. Add 10%: 401.5 square feet, which is 12.5 sheets of 4 × 8, so 13. The ceiling is 168 square feet, 184.8 with waste, so 6 sheets. Together that is 533 square feet of board: 533 ÷ 1,000 × 9 = 4.8 gallons of compound (two 4.5 gallon pails), 187 feet of tape (one 500 ft roll) and 13 × 28 + 6 × 35 = 574 screws. Switch to 4 × 12 sheets and the same room takes 9 wall sheets and 4 ceiling sheets. This room is loaded when the page opens.
Screws per sheet
The count assumes sheets hung across the framing at 16 inches on center, with a line of screws on every stud or joist the sheet crosses and screws spaced at the code maximum along it.
| Sheet | Framing members crossed | Wall (16 in apart) | Ceiling (12 in apart) |
|---|---|---|---|
| 4 × 8 ft | 7 | 28 | 35 |
| 4 × 10 ft | 8 | 32 | 40 |
| 4 × 12 ft | 10 | 40 | 50 |
What the numbers are based on
- Joint compound. USG's product FAQ says to anticipate about two 4.5 gallon pails of Sheetrock UltraLightweight All Purpose compound to finish 1,000 square feet of wallboard, and that coverage is comparable to its other ready-mixed compounds. That is 9 gallons per 1,000 square feet for taping, filling and finishing coats together.
- Tape. National Gypsum's ProForm Drywall Finishing & Repair sheet estimates 350 feet of joint tape per 1,000 square feet of wall and ceiling. The same table lists 140 lb of ready-mix compound per 1,000 square feet, which is in line with USG's two pails.
- Screws. Maximum fastener spacing comes from Table R702.3.5 of the International Residential Code: on framing 16 inches on center, screws no more than 12 inches apart on ceilings and 16 inches apart on walls. Use Type W screws long enough to go at least 5/8 inch into the wood. Local codes can be amended; your inspector has the final say.
- Waste and openings. The 10% allowance and the 21 and 15 square foot opening deductions are planning figures, not standards. Change them to suit your rooms.
Not included
- Corner bead for outside corners, measured in linear feet of corner.
- Moisture-resistant or cement board for showers and tub surrounds.
- Fire-rated 5/8 inch Type X board, which codes require in some places such as walls between a house and an attached garage.
Questions people ask
How many sheets of drywall do I need for a 12 × 14 room?
With 8 ft walls, one door and two windows, the walls are 2 × (12 + 14) × 8 = 416 square feet less 21 for the door and 30 for the windows: 365 square feet. With 10% extra that is 401.5 square feet, or 13 sheets of 4 × 8. The 168 square foot ceiling adds 6 more sheets, so 19 in all.
Should I use 4 × 8, 4 × 10 or 4 × 12 sheets?
Longer sheets mean fewer butt joints, and butt joints are the hardest seams to hide. A 12 ft sheet hung across a 12 ft wall leaves no end joints at all. The trade-off is weight and handling: a 4 × 12 sheet of 1/2 inch board is heavy for one person and may not fit up a stairway. Try each size in the calculator to see the sheet count change.
How much joint compound do I need?
USG says to plan on about two 4.5 gallon pails of its ready-mixed all-purpose compound for every 1,000 square feet of wallboard, which is about 9 gallons. The calculator uses that rate. Setting-type powders and lightweight compounds have their own coverage, so read the bag or pail.
How much drywall tape do I need?
National Gypsum's estimating table gives 350 feet of paper tape per 1,000 square feet of board. A 533 square foot room needs about 187 feet, so one 500 ft roll. Inside corners use the same paper tape folded; outside corners need corner bead, which is not included here.
How many drywall screws per sheet?
The International Residential Code, Table R702.3.5, allows screws at most 16 inches apart on walls and 12 inches apart on ceilings when framing is 16 inches on center. A 4 × 8 sheet hung across the studs crosses 7 framing members, so that is 28 screws on a wall and 35 on a ceiling. Many installers use more; this is the minimum that meets the table.
Do I subtract doors and windows?
The calculator subtracts 21 square feet per door and 15 per window, then adds 10% back for waste and offcuts. Many pros skip the deductions altogether, because a sheet with a window cut out of it still has to be bought. If you hang mostly full sheets around small openings, set the door and window counts to zero for a safer number.