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This drywall calculator works out how many sheets of drywall (also called gypsum board, plasterboard or sheetrock) you need to cover the walls and ceiling of a room. It also estimates the screws, joint compound and joint tape you will need to finish the job.
How to Use the Drywall Calculator
- Enter the room length, width and wall height.
- Enter the number of doors and windows to subtract from the wall area.
- Choose the sheet size. Larger sheets mean fewer joints to tape and finish, but they are heavier to handle.
- Add a waste allowance; 10% is typical for cuts around openings, outlets and corners.
- Tick the ceiling option if you are also covering the ceiling.
Drywall Formula
Area = 2 × (Length + Width) × Height − Openings (+ Ceiling)
Sheets = Area × (1 + Waste %) ÷ Area of one sheet, rounded up
A 4 × 8 ft sheet covers 32 sq ft, a 4 × 10 ft sheet 40 sq ft and a 4 × 12 ft sheet 48 sq ft. In metric, a 1.2 × 2.4 m board covers 2.88 m².
Worked Example: 12 × 12 ft Room with 8 ft Walls
- Wall area: 2 × (12 + 12) × 8 = 384 sq ft
- With 10% waste: 422 sq ft
- 4 × 8 sheets: 422 ÷ 32 = 13.2, so buy 14 sheets
- Adding the 144 sq ft ceiling raises the total to 19 sheets
Metric example: a 4 × 3 m room with 2.4 m walls has 33.6 m² of wall. With 10% waste that is 37 m², or 13 boards of 1.2 × 2.4 m.
Drywall Materials Rules of Thumb
| Item | Typical quantity |
|---|---|
| Screws | About 1 per sq ft of board (32 per 4 × 8 sheet), or about 11 per m² |
| Joint compound (ready-mixed) | About 140 lb per 1,000 sq ft (0.67 kg per m²) |
| Joint tape | About 370 ft per 1,000 sq ft (1.2 m per m²) |
| Corner bead | One length for each outside corner, matched to the wall height |
Ceilings usually need screws closer together than walls, and finishing quality affects how much compound you use, so treat these numbers as a guide.
Choosing Drywall Thickness
- 1/2 in (12.5 mm): standard for most interior walls.
- 5/8 in (15 mm): used for ceilings with wider joist spacing and for fire-rated assemblies such as garage walls next to living space.
- Moisture-resistant board: for bathrooms and laundry rooms, though tile areas in showers need a proper backer board.
- Check local codes for fire-rated and moisture-resistant requirements.
Drywall Tips
- Hang ceilings first, then walls, so the wall sheets support the ceiling edges.
- Hang sheets horizontally on walls; it usually means fewer seams and stronger joints.
- Stagger the end joints so they do not line up on the same stud.
- Ready to paint the new walls? Use our paint calculator next.
Frequently Asked Questions
How many sheets of drywall do I need for a 12×12 room?
For 8 ft walls, a 12 × 12 room has 384 sq ft of wall. With 10% waste you need 14 sheets of 4 × 8 drywall, or 19 sheets if you also cover the ceiling.
How many square feet are in a sheet of drywall?
A 4 × 8 sheet covers 32 sq ft, a 4 × 10 sheet covers 40 sq ft and a 4 × 12 sheet covers 48 sq ft.
How many screws do I need per sheet of drywall?
Plan on about 32 screws per 4 × 8 sheet on walls, which is about one per square foot. Ceilings may need slightly more.
How much joint compound do I need?
A common rule is about 140 lb of ready-mixed joint compound per 1,000 sq ft of drywall, which is roughly two to three 4.5-gallon buckets.
Should I subtract doors and windows from the drywall area?
Yes, but many installers subtract only part of each opening because sheets are cut around them. The waste allowance covers these offcuts.
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