Drywall Calculator

A 12x12 room with 8-foot ceilings has roughly 384 square feet of wall area plus 144 square feet of ceiling, totaling 528 square feet before subtracting openings. With a 10 percent waste factor, plan for about 580 square feet of drywall, which is approximately 18 sheets of standard 4x8 panels or 15 sheets of 4x10 panels.

Use 1/2-inch drywall for standard residential walls. For ceilings, 5/8-inch is preferred because it sags less between joists and provides better fire resistance. In garages attached to living space and between dwelling units, 5/8-inch Type X fire-rated drywall is required by building code regardless of framing direction.

Standard all-purpose joint compound needs at least 24 hours between coats in normal conditions (65 to 75 degrees Fahrenheit with good ventilation). Fast-setting or hot mud, labeled as 20-minute, 45-minute, or 90-minute compound, dries by chemical reaction rather than evaporation and can be recoated much sooner, though it cannot be sanded as easily as air-dried compound.

Greenboard is moisture-resistant drywall with a water-resistant facing, suitable for humid areas like bathrooms where it will not be directly splashed. Standard drywall absorbs moisture quickly and will deteriorate in wet conditions. Neither greenboard nor standard drywall should be used as a substrate for tile in shower enclosures; use cement board or a waterproof membrane system in direct-water applications.