What is Nominal vs Actual?

Nominal vs actual refers to the gap between what lumber is called and what it really measures. The difference catches woodworkers off guard, especially when cutting joinery.

Lumber example. A "2x4" is actually 1.5 x 3.5 inches. A "1x6" is actually 0.75 x 5.5 inches. The nominal size reflects the rough-sawn dimension before the board is dried and planed smooth. Drying shrinks the wood. Planing removes another 1/8 to 1/4 inch per face.

Common nominal vs actual sizes: - 1x4: actual 0.75 x 3.5 inches - 1x6: actual 0.75 x 5.5 inches - 1x8: actual 0.75 x 7.25 inches - 2x4: actual 1.5 x 3.5 inches - 2x6: actual 1.5 x 5.5 inches - 2x10: actual 1.5 x 9.25 inches

Plywood is different. A "3/4-inch" sheet of plywood actually measures 23/32 inch (about 18.3 mm). This matters for joinery: if you cut a 3/4-inch dado to receive a plywood shelf, the shelf will be loose by 1/32 inch. Always measure your actual sheet thickness before cutting dados or rabbets.

Why nominal vs actual matters for cut lists. Using nominal dimensions in your parts list creates compounding errors. A cabinet side listed as 3/4 inch thick but actually 23/32 inch means every dado, rabbet, and shelf dimension is wrong. Always use actual measured dimensions in your cut list.

Hardwood is sold rough. A 4/4 board (nominally 1 inch) planes down to about 13/16 inch. A 6/4 board (1.5 inches nominal) becomes about 1-5/16 inches after surfacing. Budget for this loss when planning your cut list.

SmartCutList uses the dimensions you enter, so always input actual measurements for accurate cutting diagrams and material estimates.