How to estimate drywall
Add wall area (perimeter × height) to ceiling area (length × width). Don't subtract small doors and windows—offcuts rarely fit elsewhere, and the extra covers breakage. Divide by sheet area: 32 sq ft for 4×8, 48 sq ft for 4×12.
Example: a 12 × 12 ft room with 8 ft walls: 48 × 8 = 384 + 144 ceiling = 528 sq ft. With 10% waste, 580.8 sq ft ÷ 32 = 18.2 → 19 sheets of 4×8.
Which thickness?
- 1/2 in: standard for interior walls on studs 16 in on center
- 5/8 in (Type X): ceilings with 24 in joists, garages adjoining living space, and fire-rated assemblies where code requires it
- Moisture-resistant board for bathrooms (not as a tile backer in showers—use cement board there)
Finishing materials
Plan on roughly 0.05 gallons of all-purpose joint compound per square foot for three coats and about one drywall screw per square foot. Longer 12 ft sheets mean fewer butt joints and less taping.