How to use the drywall calculator
- Enter the room size and tick the ceiling if you are covering it.
- Count doors and windows to subtract.
- Pick a sheet size. The table compares all sizes.
- Read the sheets, compound, tape and screws, and add prices for a total.
The drywall formula
Walls = 2 × (length + width) × height − openings
Ceiling = length × width
Sheets = area × (1 + waste) ÷ sheet area, rounded up
Compound ≈ 9.4 gal per 1,000 sq ft; tape ≈ 370 ft per 1,000 sq ft; screws ≈ 1 per sq ft
Worked example
A 12 × 14 ft room, 8 ft walls, with ceiling
- Walls 416 sq ft − door 21 − windows 30 = 365 sq ft; ceiling 168 sq ft; total 533 sq ft.
- With 10% waste: 586 sq ft ÷ 32 = 18.3, so 19 sheets of 4 × 8.
- Compound 5 gal = 2 boxes; tape 197 ft = 1 roll; about 533 screws.
Sheets by room size (walls only, 8 ft, 4 × 8 sheets, 10% waste)
| Room | Wall area | Sheets |
|---|---|---|
| 10 × 10 ft | 320 sq ft | 11 |
| 12 × 12 ft | 384 sq ft | 14 |
| 12 × 14 ft | 416 sq ft | 15 |
| 14 × 16 ft | 480 sq ft | 17 |
| 16 × 20 ft | 576 sq ft | 20 |
Before subtracting doors and windows.
Common mistakes to avoid
- No waste allowance. Cut-outs and offcuts add up fast.
- Joints lined up. Stagger end joints between rows.
- Wrong board in wet areas. Use moisture-resistant or cement board where required.
- Running out of mud mid-coat. Three coats use more than people expect.
Frequently asked questions
How many sheets of drywall do I need for a 12 × 14 room?
With 8 ft walls: 416 sq ft of wall, less a door and two windows = 365 sq ft, plus a 168 sq ft ceiling = 533 sq ft. With 10% waste that is 586 sq ft, or 19 sheets of 4 × 8.
Should I subtract doors and windows?
Subtract them, but expect less saving than their area, because openings are cut out of full sheets. That is why we add 10% waste.
Which sheet size should I use?
4 × 8 is easiest to carry and fits most cars. 4 × 12 sheets reduce the number of joints to tape, which saves finishing time, but they are heavy and need two people.
How much joint compound do I need?
Roughly 9 to 10 gallons of ready-mix per 1,000 sq ft for taping and two finish coats: about two 4.5 gallon boxes for a 12 × 14 room with ceiling.
How many screws per sheet of drywall?
About 28 to 32 per 4 × 8 sheet on walls with studs 16 in apart, and a few more on ceilings: roughly one screw per square foot.
What thickness of drywall should I use?
1/2 in is standard for walls; 5/8 in is common on ceilings and where fire-rated board is required, such as garage walls next to living space. Check your local code.