Plywood: Nominal vs. Actual Thickness

How to ensure accuracy when building projects with plywood

Hello and welcome to Joe Shows How! Most DIYers know that construction lumber is referred to by its nominal dimension, not its actual dimension. For example, a 2x4 doesn’t measure 2 in. x 4 in., it’s actually 1 1/2 in. x 3 1/2. And a 1x6 is only 3/4 in. thick x 5 1/2 in. wide. But not many people know that some types of plywood are also known by a nominal dimension.

Most 3/4-in.-thick plywood is actually only 11/16 or 21/32 in. thick. Now that might not seem like much, but it can be critical when constructing a drawer or cabinet to fit snugly into a space. So, when setting one plywood part between two others—such as when placing a drawer back between the two drawer sides—here’s how to measure for a perfect fit: Let’s say you’re building a 10-in.-wide drawer. Clamp together the two plywood drawer sides, then set the 10 in. graduation line of your tape measure on the edge of the clamped together parts. Now simply read the dimension on the opposite edge, and cut the drawer back to that size.

Nominal plywood dimensions also come into play when routing dados, grooves, rabbets and other wood joints. For example, if you use a 3/4-in. straight bit to rout a dado to accept a 3/4-in. plywood shelf, the shelf won’t fit tightly into the dado because it’s not actually 3/4 in. thick. Avoid this problem by cutting the dado with an undersized plywood bit, which is specifically made to produce tight-fitting plywood joints.

I hope these tips help elevate your woodworking skills!