Drywall Calculator

How to calculate drywall

Wall area = 2 × (length + width) × height Sheets = (wall area + ceiling − openings) × (1 + waste) ÷ sheet area

A standard door takes away about 21 sq ft (3 × 7 ft) and a typical window about 15 sq ft (3 × 5 ft). A 4 × 8 sheet covers 32 sq ft and a 4 × 12 sheet covers 48 sq ft.

Worked example

A 12 × 14 ft room with 8 ft ceilings has 416 sq ft of wall and a 168 sq ft ceiling. Removing one door and two windows (51 sq ft) leaves 533 sq ft. With 10% waste that is 586.3 sq ft, or 19 sheets of 4 × 8 drywall.

Choosing sheet size and thickness

• Larger 4 × 12 sheets mean fewer seams but are heavier to handle.
• 1/2-inch drywall is standard for walls; 5/8-inch is common for ceilings and fire-rated walls.
• Use moisture-resistant board in bathrooms and laundry rooms.

Material estimates are approximate. Check local building codes for fire-rated and moisture-resistant requirements.

Frequently asked questions

How many sheets of drywall for a 12×12 room?

With 8 ft walls, about 12 sheets of 4 × 8 for the walls and 5 more for the ceiling, before subtracting openings.

How much does a sheet of drywall cover?

A 4 × 8 sheet covers 32 sq ft, a 4 × 10 covers 40 sq ft and a 4 × 12 covers 48 sq ft.

Should I subtract doors and windows?

Yes, but many installers subtract only part of the openings because offcuts are rarely reusable.

How much waste should I allow?

About 10–15%, more for rooms with many corners or angles.