Drywall Calculator

Drywall is sold in 4-foot-wide sheets in lengths of 8, 10, 12, and 16 feet. The standard 4×8 sheet is the go-to for most DIY projects — it's manageable to handle alone and available everywhere. Longer sheets (4×12 or 4×16) reduce the number of horizontal butt joints, which are the hardest seams to finish invisibly, but are heavier and require careful planning to avoid wasted material on short walls. For 9-foot ceilings, 4×9 sheets eliminate the horizontal mid-wall seam that appears when stacking 8-foot sheets.

Different drywall types serve different applications. Standard ½-inch gypsum board is used for interior walls and ceilings. 5/8-inch Type X board is required in walls separating garages from living space and in fire-rated assemblies — this is a building code requirement, not a suggestion. Moisture-resistant board (green board) is suitable for bathroom walls but should not be used as tile backer in wet areas like showers — use cement board (HardieBacker, Durock, or similar) anywhere tile will be continuously wetted. Using the wrong type is a code violation that inspectors will flag and that can cause premature failure.

The hidden costs of drywall are in the finishing materials. Joint compound — often called "drywall mud," not to be confused with the sand-cement "deck mud" used under tile — is applied in three coats over tape and fasteners. Plan on roughly one 4.5-gallon bucket of all-purpose compound per 100 square feet for a three-coat finish. Use paper tape on flat joints for strength; self-adhesive fiberglass mesh tape is easier but weaker and prone to cracking at butt joints. Metal or vinyl corner bead protects every outside corner. Sand between coats with 120-grit paper, and always prime before painting (use the Paint Calculator to estimate gallons for the finish coats) — bare joint compound absorbs paint unevenly and creates visible lap marks that no amount of additional paint will fully hide.