Plywood Calculator

CDX is construction-grade plywood with one C-face (knots allowed, plugged), one D-face (rough, unfilled knots), and exterior (“X”) glue. It’s the standard for wall sheathing, roof decking, and subfloor where the surface will be covered. Sanded plywood(BC or AC) has at least one smooth, sanded face suitable for visible applications like cabinet boxes, shelving, and furniture. AC has one A-grade face (smooth, no defects) and one C-grade back. BC is slightly lower grade on the face. Sanded plywood costs 50–100% more than CDX.

Use 3/4” (23/32” actual) tongue-and-groove plywood for residential subfloor over joists spaced 16” on center. For 19.2” or 24” joist spacing, some codes require 7/8” or 1” panels. Never use 1/2” plywood for subfloor — it will flex and bounce underfoot, causing finish flooring problems. CDX or structural-rated panels (APA-rated Sturd-I-Floor) are both acceptable. Always glue and screw to joists to eliminate squeaks.

Divide the wall area (length × height) by the sheet area. For an 8-ft wall, standard 4×8 sheets install vertically with no horizontal cuts. A 24-ft long, 8-ft tall wall = 192 sqft ÷ 32 sqft/sheet = 6 sheets. For 9 or 10-ft walls, consider 4×10 sheets to avoid a horizontal seam. Add 10% waste for cuts around windows and doors. Sheathing typically uses 1/2” CDX with nails (not screws) per building code for lateral bracing.

Use longer sheets when the height or span exceeds 8 feet. Common scenarios: 9 or 10-ft wall sheathing (4×10 eliminates the horizontal seam and blocking), tall gable walls, and large subfloor areas where fewer joints mean less squeaking. The cost per sqft is similar, but longer sheets are heavier and harder to handle — a 4×12 sheet of 3/4” plywood weighs about 100 lbs. For roof decking on long rafter runs, 4×10 sheets can reduce the number of butt joints on the sheathing.