How the math works
Perimeter: 2 × (16 + 20) = 72 ftWall area: 72 × 8 ft = 576 sq ftCeiling: 16 × 20 = 320 sq ftTotal × 1.10 waste = 985.6 sq ft4x8 sheets: ÷ 32 = 31; 4x12 sheets: ÷ 48 = 21
Don’t subtract doors and windows on small rooms — the cut-offs rarely get reused. On big rooms subtract openings over 50 sq ft.
Trade pro tips
- Hang the ceiling first, then walls top row first so the factory edge meets the ceiling.
- Use 1/2" on walls; 5/8" or 1/2" ceiling board on ceilings framed 24" OC.
- Stagger end joints and keep them off door and window corners.
Frequently asked questions
How many sheets of drywall for a 16x20 room?
31 sheets of 4x8 for walls and ceiling with 8' walls (20 for walls only), including 10% waste.
How many 4x12 drywall sheets for a 16x20 room?
21 sheets of 4x12 for walls and ceiling — fewer seams to tape than 31 4x8s.
How much mud and tape for a 16x20 room?
About 332 ft of paper tape and 2 × 4.5-gallon buckets of all-purpose compound for three coats.
How many drywall screws for a 16x20 room?
Roughly 896 1-1/4" screws (about one per sq ft at 16" OC framing) — a 5 lb box is plenty.