Drywall Calculator
List each wall and ceiling, subtract doors and windows, choose a sheet size and waste allowance, and get the number of drywall sheets plus screws, joint compound and tape for the job, in feet or metres.
Walls and ceilings
Openings to deduct
Sheets and extras
How to use the Drywall Calculator
- Choose feet or metres at the top.
- Enter each wall as length × height and each ceiling as length × width. Use Qty for identical walls, and add or remove rows as needed.
- Enter the doors and windows and their typical size so their area is deducted.
- Pick the sheet size and waste allowance (10% is typical; use 15% for rooms with many corners and cut-outs).
- Press Calculate to see the sheets, screws, joint compound and tape, then copy the materials list.
Drywall formulas
- Wall area = length × height × number of identical walls. Ceiling area = length × width.
- Net area = total area − (doors × door area) − (windows × window area).
- Sheets = net area × (1 + waste %) ÷ sheet area, rounded up.
- Screws ≈ sheets × 32. Compound ≈ net ft² ÷ 100 gallons. Tape ≈ net ft² × 0.37 ft.
Worked example: a 12 × 10 ft bedroom
- Walls: 2 × (12 × 8) + 2 × (10 × 8) = 192 + 160 = 352 ft². Ceiling: 12 × 10 = 120 ft². Total 472 ft².
- Openings: one 3 × 7 door (21 ft²) and two 3 × 4 windows (24 ft²) = 45 ft². Net area 427 ft².
- Add 10% waste: 427 × 1.10 = 469.7 ft². With 4×8 sheets: 469.7 ÷ 32 = 14.7, so 15 sheets.
- Screws: 15 × 32 = 480. Compound: 427 ÷ 100 ≈ 4.3 gallons (one 4.5-gal bucket). Tape: 427 × 0.37 ≈ 158 ft (one 250-ft roll).
Drywall sheet sizes and coverage
| Sheet | Coverage | Typical use | Sheets per 100 ft² (no waste) |
|---|---|---|---|
| 4 × 8 ft | 32 ft² (2.97 m²) | Standard walls, DIY, small rooms | 3.1 |
| 4 × 10 ft | 40 ft² (3.72 m²) | 9 ft ceilings hung horizontally, fewer seams | 2.5 |
| 4 × 12 ft | 48 ft² (4.46 m²) | Long walls and ceilings, professional crews | 2.1 |
| 1.2 × 2.4 m | 2.88 m² | Standard metric plasterboard | 0.35 per m² |
Thickness: 1/2 in (12.5 mm) is standard for walls, 5/8 in (15 mm) type X is used for fire-rated walls, garages and ceilings with joists 24 in apart, and moisture-resistant board is used in bathrooms.
Frequently asked questions
How many sheets of drywall do I need for a 12×12 room?
A 12 × 12 ft room with 8 ft walls has 4 × 12 × 8 = 384 ft² of wall. Subtract a 3 × 7 ft door (21 ft²) to get 363 ft², add 10% waste for 399.3 ft², and divide by 32 ft² per 4×8 sheet: 12.5, so buy 13 sheets. The 144 ft² ceiling needs another 5 sheets with waste.
How do you calculate drywall sheets?
Add up the area of every wall (length × height) and ceiling (length × width), subtract doors and windows, multiply by 1 plus the waste percentage, then divide by the area of one sheet and round up. A 4×8 sheet covers 32 ft², a 4×10 covers 40 ft² and a 4×12 covers 48 ft².
How many screws per sheet of drywall?
About 32 screws for a 4×8 sheet on walls with studs 16 inches on center, spaced roughly every 12 to 16 inches. Ceilings and 4×12 sheets need more, often 40 to 48, so raise the screws-per-sheet value.
How much joint compound do I need?
A common rule is about 1 gallon of ready-mixed compound per 100 ft² of drywall for taping plus two finish coats, so a 4.5-gallon bucket finishes roughly 450 ft². Smooth Level 5 finishes use more.
How much drywall tape do I need?
Plan on about 370 feet of tape per 1,000 ft² of drywall, which is roughly 0.37 ft of tape per square foot. A standard paper tape roll is 250 or 500 ft.
Should I deduct doors and windows?
Yes for large openings, but many installers deduct only part of each opening because the offcuts are rarely usable. If you deduct everything, keep a 10 to 15% waste allowance.
Is 4×12 drywall better than 4×8?
Longer sheets mean fewer butt joints and less taping, so 4×12 sheets are faster to finish on long walls and ceilings, but they are heavy and awkward for one person. 4×8 sheets are easier to carry and fit in most vehicles.