Drywall Calculator

This calculator counts walls and ceilings separately. Walls are 2 × (length + width) × height; the ceiling is length × width. Add a waste factor to each, then divide by the sheet size. For a 12×12 room with 8 ft walls you have 384 sq ft of walls (→ 14 sheets of 4×8 at 10% waste) plus a 144 sq ft ceiling (→ 5 sheets), for 19 sheets total.

Interior walls are usually 1/2 inch. Ceilings are commonly 5/8 inch because the extra thickness resists sagging between joists and adds fire resistance; 1/2 inch sag-resistant ("ceiling board") is also used, especially on 24-inch joist spacing. 5/8 inch "Type X" is also required on garage walls and ceilings and other fire-rated assemblies. Because the two surfaces often use different boards, this calculator gives you a separate sheet count for each.

4×8 ft sheets (32 sq ft) are the easiest to handle and work well in standard 8 ft rooms. Larger 4×9 or 4×12 sheets reduce the number of seams—ideal for taller walls and ceilings—but are heavy and usually need two people. You can set a different sheet size for walls and ceilings here.

A 10% waste allowance is standard for simple rectangular rooms. Increase to 15% for rooms with multiple windows and doors, and up to 20% for rooms with complex angles, archways, or many cutouts. Extra sheets also help you match texture or board type if you need to patch later.