How the drywall calculator works
It adds up the area of all four walls, takes out a standard allowance for each door and window, adds the ceiling if you’re boarding it, then adds a waste allowance for cuts. That total is divided by the area of one sheet and rounded up.
Finishing materials are estimated from the board area using common trade rules of thumb, so treat them as a shopping-list starting point.
The formula
wall area = 2 × (length + width) × height
openings = doors × 20 ft² + windows × 15 ft²
board area = wall area − openings (+ length × width for the ceiling)
sheets = board area × (1 + waste %) ÷ sheet area, rounded up
A 4×8 sheet covers 32 ft² (2.97 m²), a 4×10 covers 40 ft² and a 4×12 covers 48 ft².
Tips
- Use the longest sheets you can carry and fit through the door. Fewer sheets means fewer seams to tape, which saves more time than it costs.
- 10% waste suits most rectangular rooms. Go to 15% for rooms with lots of corners, bulkheads or sloped ceilings.
- Basements: use mould-resistant board on exterior walls. In bathrooms, use moisture-resistant board or cement board behind tile.
- Ceilings: 1/2” sag-resistant board (or 5/8”) is usually the right choice. Check what your local code requires for garages and fire separations.