Drywall Calculator
Enter the size of a wall or a room, take off the doors and windows, pick a sheet size and add a waste allowance. The calculator gives the area to cover and the number of sheets, rounded up.
Last updated November 4, 2026
Total area to subtract. A typical interior door is about 20 sq ft (1.9 m²).
10% is a common starting point for cuts and breakage.
Result
13 sheets of 4 x 8 ft
| Measure | Value |
|---|---|
| Wall area | 352 sq ft |
| Area to cover | 352 sq ft |
| With 10% waste | 387.2 sq ft |
| Sheets (rounded up) | 13 |
| Spare board | 64 sq ft |
Area method only: it does not lay out sheets, so seams and cuts can change the count. Check with your supplier.
Show the work
Formula: sheets = ceil((walls + ceiling - openings) x (1 + waste / 100) / sheet area); walls = 2 x (length + width) x height
- Walls: 2 x (12 + 10) x 8 = 352 sq ft.
- Area to cover: 352 + 0 - 0 openings = 352 sq ft.
- Waste: 352 x (1 + 10 / 100) = 387.2 sq ft.
- Sheets: 387.2 / 32 sq ft per 4 x 8 ft sheet, rounded up = 13.
Result: 13 sheets of 4 x 8 ft
How the number of sheets is worked out
area = 2 × (length + width) × height + ceiling − openings
sheets = ceil( area × (1 + waste ÷ 100) ÷ sheet area )
A room has four walls, so the wall area is twice the length plus the width, times the height. The ceiling, if included, is length times width. Openings are subtracted as one total area, then the waste allowance is added and the result is divided by the area of one sheet and rounded up.
A 12 ft by 10 ft room with 8 ft walls has 2 × (12 + 10) × 8 = 352 sq ft of wall. With 10 percent waste that is 387.2 sq ft. A 4 x 8 ft sheet covers 32 sq ft, so 387.2 ÷ 32 = 12.1, which rounds up to 13 sheets.
See how we calculate for the formulas, sources and review schedule behind every calculator.
Sheet sizes
Choose 4 x 8, 4 x 10 or 4 x 12 ft, or 1.2 x 2.4 m. Longer sheets mean fewer seams but are harder to carry. The calculator compares areas only, so it does not lay out the sheets or check where seams fall.
Doors and windows
Enter the total area of all openings. A typical interior door is about 20 sq ft. Many installers still count small openings as solid wall because of the extra cutting, so subtract only large ones if you are unsure.
How to use the Drywall Calculator
- Choose imperial or metric and whether to cover a room or one wall.
- Enter the length, width and wall height, and add the ceiling if needed.
- Enter the total area of doors and windows, or leave it blank.
- Pick the sheet size and a waste percentage.
- Read the sheets to buy, then use Copy, Print or Share.
Worked example
A 12 ft by 10 ft room with 8 ft walls has 352 sq ft of wall. With 10 percent waste, 4 x 8 ft sheets and no openings, it needs 387.2 ÷ 32 = 12.1, so 13 sheets.
| Case | Sheet | Sheets |
|---|---|---|
| Walls only | 4 x 8 ft | 13 |
| Walls, 40 sq ft of openings | 4 x 8 ft | 11 |
| Walls and ceiling, 40 sq ft of openings | 4 x 8 ft | 15 |
| Walls and ceiling, 40 sq ft of openings | 4 x 12 ft | 10 |
Frequently asked questions
How many sheets of drywall do I need for a room?
Add the four walls, and the ceiling if you are covering it. A 12 ft by 10 ft room with 8 ft walls needs 13 sheets of 4 x 8 ft at 10 percent waste.
How much waste should I allow for drywall?
Ten percent is a common starting point for cuts and breakage. Rooms with many corners or openings may need more, so confirm with your installer.
Does this include joint compound, screws or tape?
No. It counts sheets only, because those amounts depend on the product and the finish level. Check the packaging for coverage.
Should I subtract windows and doors?
You can subtract their total area, but small openings are often left in because cutting around them wastes board. Large openings are worth subtracting.