What the Drywall Calculator does
This calculator estimates the drywall - plasterboard in the UK - for a room: the wall and ceiling area minus doors and windows, the number of sheets of the size you buy with a waste allowance, and the screws, joint tape and compound to hang and finish them, with a cost total if you enter prices. Feet and 4 x 8 or 4 x 12 sheets, or metres and 1200 x 2400 mm boards, both work.
Every quantity shows how it was worked out, and the fixing and finishing rules of thumb are dated, sourced and editable, so you can match them to the board maker's instructions.
How to use it
- Choose feet or metres and enter the room's length, width and wall height. Tick walls, ceiling or both.
- Add each door and window. Typical sizes are filled in (a 3 ft x 6 ft 9 in door, a 0.9 x 2.1 m door) - overwrite them with your own measurements and set how many of each. Add any extra area, such as a bulkhead.
- Pick the sheet size you will buy and a waste allowance: about 10% for a plain room, 15% for lots of openings, angles or short walls.
- Read the number of sheets, then the screws, tape and compound. Open "Prices" to get a cost estimate, and "Fixing and finishing rules" to change stud spacing, screw spacing, roll length or bucket size.
Reading the results
Sheets are counted separately for walls and ceiling and rounded up, because offcuts from one rarely suit the other. The waste allowance covers cuts around openings and mistakes; it is added before rounding.
Openings are subtracted in full. Some installers board straight over small windows and cut them out afterwards, which uses more board; if you hang that way, enter fewer openings or a higher waste figure.
Screw counts follow the fixing pattern: one line of screws on every stud or joist a sheet crosses, with screws every 16 in on walls and 12 in on ceilings (ASTM C840 maximums), or 300 mm and 230 mm on 600 mm studs (British Gypsum). A 4 x 8 sheet on a wall takes about 28 screws; on a ceiling about 35.
Worked example: a 12 x 10 ft bedroom, walls and ceiling
Walls are 2 x (12 + 10) x 8 = 352 sq ft. One door (3 x 6.75 = 20.25 sq ft) and two windows (3 x 4 = 12 sq ft each) take off 44.25, leaving 307.75 sq ft. The ceiling is 12 x 10 = 120 sq ft.
With 4 x 8 sheets (32 sq ft) and 10% waste: walls 307.75 x 1.1 / 32 = 10.6, so 11 sheets; ceiling 132 / 32 = 4.1, so 5 sheets - 16 in all. Screws: 11 x 28 + 5 x 35 = 483. Tape: 427.75 sq ft x 0.37 = 158 ft, one 250 ft roll. Compound: 427.75 x 0.009 = 3.85 gallons, one 4.5 gallon bucket. At 15 a sheet, 12 a box of screws, 6 a roll and 20 a bucket the materials come to 278.
Formulas and scoring rules
- Areas
walls = 2 x (length + width) x height - openings + extra; ceiling = length x width- Sheets
sheets = ceil(area x (1 + waste / 100) / sheet area), walls and ceiling separately- Screws per sheet
(floor(across / framing spacing) + 1) x (floor(along / screw spacing) + 1)Walls: the short side runs across the studs. Ceilings: the long side runs across the joists.- Joint tape
tape = board area x 0.37 ft per sq ft (1.214 m per m2)USG's published coverage of about 370 ft of tape per 1,000 sq ft of board.- Joint compound
compound = board area x 0.009 US gal per sq ft (0.367 L per m2)About two 4.5 gallon pails of USG ready-mixed lightweight compound per 1,000 sq ft. Heavier all-purpose compounds and a fourth coat use more.
Limitations: what the result does not prove
- It is an estimate for buying materials, not a cutting plan. Sheet layout, stagger and where joints fall can change the count by a sheet or two in awkward rooms.
- Rules of thumb vary by product: tape and compound coverage depend on the joint layout, the number of coats and the finisher. Check the coverage printed on the products you buy.
- Fire-rated, moisture-resistant, acoustic and two-layer systems have their own fixing schedules, and building codes may require specific board types in bathrooms, garages and between dwellings.
- It does not include corner bead, adhesive, insulation, sanding or primer, or labour.
Privacy: where your data goes
Everything you paste, type or drop is processed in this browser tab. It is not uploaded, logged, stored or sent to analytics. Session recording and tag-manager scripts are switched off on this page.
Standards and sources
- ASTM C840 - Standard Specification for Application and Finishing of Gypsum Board
- USG - Joint tape product data (coverage per 1000 sq ft)
- British Gypsum - The White Book
Frequently asked questions
How many sheets of drywall do I need for a room?
Work out the wall area (perimeter x height), subtract doors and windows, add the ceiling if you are boarding it, add about 10% for waste and divide by the sheet area - 32 sq ft for a 4 x 8 sheet. A typical 12 x 10 ft bedroom with 8 ft walls needs about 16 sheets for walls and ceiling.
How many screws do I need per sheet of drywall?
About 28 for a 4 x 8 sheet on a wall with studs at 16 in and screws every 16 in, and about 35 on a ceiling with screws every 12 in. That is roughly one screw per square foot; change the spacing to match your fixing schedule.
How much joint compound do I need?
A common estimate is about 9 gallons of ready-mixed compound per 1,000 sq ft of board, roughly two 4.5 gallon buckets. A single 12 x 10 ft room with a ceiling needs about 4 gallons.
Should I use 4 x 8 or 4 x 12 drywall sheets?
Longer sheets mean fewer joints to tape and finish, which saves time and compound, but they are heavier and harder to carry and lift. 4 x 12 suits long walls and ceilings when two people are hanging; 4 x 8 is easier alone.
How many plasterboard sheets do I need for a ceiling?
Divide the ceiling area by the board area and add waste: a 4 x 3.2 m ceiling is 12.8 m2, plus 12% is 14.3 m2, which needs 5 boards of 1200 x 2400 mm (2.88 m2 each). Tick only Ceiling to get the figure.
Do I subtract doors and windows when estimating drywall?
Usually yes - this calculator subtracts every opening you list. Some installers ignore small windows because the offcuts are rarely usable; if you do, raise the waste allowance instead of removing the window from the list.
How much tape do I need for drywall?
About 370 ft of paper tape per 1,000 sq ft of board, which is about 0.37 ft per sq ft or 1.2 m per m2. A 250 ft roll covers roughly 675 sq ft of board.
Last reviewed by the A2Z.Tools team against the sources listed above.
