How the drywall calculator works
Drywall is bought by the sheet. The calculator takes the net wall area (perimeter × height minus openings), adds your allowance for cuts and breakage, divides by the area of one sheet, and rounds up.
Change the sheet length to compare 4 × 8 and 4 × 12 sheets: longer sheets mean fewer pieces and fewer seams to tape, but they are heavier to handle.
Formula and assumptions
- H
- wall height
- openings
- doors and windows
Assumptions and limits
- Walls only. Calculate ceilings as their own area.
- An area estimate, not a sheet layout. Odd heights can create more waste.
Worked example
A 12 × 10 ft room with 8 ft walls, 20 sq ft of openings, 4 × 8 ft sheets, 10% waste.
- Net wall area = 352 − 20 = 332 sq ft.
- 332 × 1.10 = 365.2 sq ft.
- 365.2 ÷ 32 = 11.41; round up to 12 sheets.
These are the calculator’s default values, so the live result above matches this example until you change an input.
How to measure correctly
- Measure wall height; 8 ft walls suit 4 × 8 sheets hung horizontally in two rows.
- Measure the ceiling separately if it will be boarded.
- Note outside corners and openings that need corner bead.
Sheets for the example room
| Sheet size | Area per sheet | Sheets, no waste | Sheets + 10% |
|---|---|---|---|
| 4 × 8 ft | 32 sq ft | 11 | 12 |
| 4 × 10 ft | 40 sq ft | 9 | 10 |
| 4 × 12 ft | 48 sq ft | 7 | 8 |
Drywall Calculator FAQ
How many sheets of drywall do I need for a 12×12 room?
With 8 ft walls, the perimeter is 48 ft and the gross wall area is 384 sq ft. Before subtracting openings and with no waste, that is exactly 12 sheets of 4 × 8. Add your openings and allowance in the calculator.
How many square feet is a sheet of drywall?
Width times length: a 4 × 8 ft sheet is 32 sq ft, 4 × 10 ft is 40 sq ft, and 4 × 12 ft is 48 sq ft.
Should I use 4×8 or 4×12 sheets?
Longer sheets reduce the number of joints to tape and finish, which saves time and gives a flatter wall. Shorter sheets are easier to carry and fit through tight spaces.
Do I subtract windows and doors?
Subtract large openings. Many installers board over small openings and cut them out, so a modest allowance covers that waste.
How much extra drywall should I buy?
A 10–15% allowance is a common planning buffer for cuts and breakage; complex rooms with many corners may need more.
Does the estimate include the ceiling?
No. Use the square footage calculator for the ceiling area and divide by sheet area.