How much drywall should I buy?
Type the size of the room and pick a sheet size. The drywall calculator subtracts doors and windows, adds an extra share for waste, and shows how many sheets to buy.
- Sheets to buy
- 13
For 366 ft² of drywall, the sheets to buy come to 13 (12.58 before rounding up).
- Sheets, not rounded
- 12.58
- Area to cover, ft²
- 366
- Area to cover, m²
- 34
Sheets to buy: 13. For 366 ft² of drywall, the sheets to buy come to 13 (12.58 before rounding up).
How to calculate
Computes how many sheets of drywall (sheetrock, gypsum board) cover a room’s walls, and its ceiling if chosen, less doors and windows, with an extra share for waste.
Example with the default inputs (Room length 12 ft, Room width 14 ft, Wall height 8 ft, Sheet size 4 × 8 ft, Extra for waste 10%, Doors 1, Area of one door 20 ft², Windows 2, Area of one window 15 ft², Cover the ceiling too No): For 366 ft² of drywall, the sheets to buy come to 13 (12.58 before rounding up).
Method: Area = 2 × (length + width) × height − doors × door area − windows × window area (+ length × width for the ceiling); sheets = area × (1 + extra ÷ 100) ÷ sheet area, rounded up.
- The room is a rectangle with walls of one height; door and window openings are not covered.
- By default a door opening is 20 ft² (36 × 80 in) and a window 15 ft² (3 × 5 ft).
- Extra for waste is 10% by default, for cut-offs around openings and at wall ends.
- Sheets are counted by area; the count does not plan where each seam falls.
Worked examples
Each example is checked against the calculator on every build.
- Room length 12 ft, Room width 14 ft, Wall height 8 ft, Sheet size 4 × 8 ft, Extra for waste 10%, Doors 1, Area of one door 20 ft², Windows 2, Area of one window 15 ft², Cover the ceiling too no gives Area to cover, ft² 366, Sheets, not rounded 12.58125, Sheets to buy 13.Source: NIST Handbook 44, Appendix C (1 ft = 0.3048 m)
- Room length 12 ft, Room width 12 ft, Wall height 8 ft, Sheet size 4 × 12 ft, Extra for waste 0%, Doors 0, Area of one door 20 ft², Windows 0, Area of one window 15 ft², Cover the ceiling too yes gives Area to cover, ft² 528, Sheets, not rounded 11, Sheets to buy 11.Source: 2 × 24 × 8 + 144 = 528 ft² ÷ 48 = 11 sheets (NIST Handbook 44 units)
- Room length 13.12 ft, Room width 9.843 ft, Wall height 8.202 ft, Sheet size 1200 × 2400 mm, Extra for waste 10%, Doors 1, Area of one door 19.38 ft², Windows 1, Area of one window 16.15 ft², Cover the ceiling too no gives Area to cover, m² 31.7, Sheets, not rounded 12.107639, Sheets to buy 13.Source: 2 × 7 × 2.5 − 1.8 − 1.5 = 31.7 m² × 1.1 ÷ 2.88 = 12.11, so 13 sheets (NIST Handbook 44 units)
How it works
- Wall area = 2 × (length + width) × height
- Openings = doors × area of one door + windows × area of one window
- Area to cover = wall area − openings (+ length × width with the ceiling)
- Sheets = area to cover × (1 + extra ÷ 100) ÷ area of one sheet
- Sheets to buy = sheets rounded up to a whole number
The sheet sizes, width × length: 4 × 8 ft (32 ft²), 4 × 9 ft (36 ft²), 4 × 10 ft (40 ft²), 4 × 12 ft (48 ft²), 54 in × 12 ft (54 ft²), 1200 × 2400 mm (2.88 m²) and 1200 × 2700 mm (3.24 m²).
Exact arithmetic. Each size is read as the exact decimal you typed, in the unit you typed it in (12 ft 6 in is exactly 150 in). The page stores a size as a number in metres or square metres and reads it back as the decimal with the fewest significant digits, in one of the box's units, that gives the same stored number; a feet-and-inches pair counts by its value in inches (12 ft 6 in counts as 150, and 426.72 cm, exactly 14 ft, stays 426.72 cm), and on a tie the unit listed first in the box's unit menu wins. Every step is exact, so a room of exactly 11 sheets gives 11, not 12.
Rounding. The areas and the unrounded sheets show with at most 2 decimals, rounded half up from the exact value, with trailing zeros left off. Sheets to buy are rounded up.
No answer. When the doors and windows add up to the whole wall area or more, the calculator shows: "The doors and windows add up to at least the whole wall area."
Assumptions
- The room is a rectangle with walls of one height; openings are not covered.
- A door is 20 ft² and a window 15 ft² unless you type other sizes.
- The extra for waste is 10% by default, from 0% to 100%.
- Sheets are counted by area; the count does not lay out each seam.
- Lengths are more than 0 and at most 1,000 m; opening areas from 0 to 10,000 m²; 0 to 100 doors and windows.
Worked examples by hand
A 12 × 14 ft room, 8 ft walls, one door, two windows, 4 × 8 ft sheets, 10% extra. 2 × 26 × 8 = 416 ft²; less 20 + 30 = 366 ft². 366 × 1.1 ÷ 32 = 12.58 sheets, so buy 13.
A 12 × 12 ft room with the ceiling, 4 × 12 ft sheets, no extra. 2 × 24 × 8 + 12 × 12 = 528 ft²; 528 ÷ 48 = 11 sheets exactly.
A 4 × 3 m room, 2.5 m walls, a 1.8 m² door, a 1.5 m² window, 1200 × 2400 mm sheets, 10% extra. 2 × 7 × 2.5 − 3.3 = 31.7 m²; 31.7 × 1.1 ÷ 2.88 = 12.11, so buy 13.
Other questions people ask
How do I calculate how much drywall I need?
Find the wall area: 2 × (length + width) × height. Subtract doors and windows, add the ceiling if you are covering it, add about 10% for waste, and divide by the area of one sheet. A 12 × 14 ft room with 8 ft walls, one door and two windows has 366 ft²; 366 × 1.1 ÷ 32 = 12.58, so 13 sheets of 4 × 8 ft.
How many square feet are in a sheet of drywall?
Width × length: a 4 × 8 ft sheet is 32 ft², 4 × 10 ft is 40 ft², 4 × 12 ft is 48 ft², and a 54 in × 12 ft sheet is 54 ft². A metric 1200 × 2400 mm sheet is 2.88 m² (31.0 ft²).
Should I use 4 × 8 or 4 × 12 sheets?
Longer sheets mean fewer seams to tape on long walls and ceilings, but they are heavier and harder to carry. The count by area is about the same; pick the size you can handle and that fits your walls. 54 in wide sheets suit 9 ft walls with fewer seams.
How much extra drywall should I buy?
The calculator adds 10% by default for pieces cut off around doors, windows and wall ends. A room with many openings, angles or short walls may need more. Set the extra to 0% for the covered area alone.
Do I subtract doors and windows?
Yes. The calculator takes 20 ft² for each door (36 × 80 in) and 15 ft² for each window (3 × 5 ft) by default; type your own sizes for a closer answer. Small openings are often covered and cut out later, so some builders do not subtract them.
How do I include the ceiling?
Turn on “Cover the ceiling too”. The calculator adds length × width. A 12 × 12 ft room with 8 ft walls and the ceiling is 384 + 144 = 528 ft², exactly 11 sheets of 4 × 12 ft with no extra.