Lumber 101: Understanding Lumber Sizing

We are back with another Lumber 101 to answer a popular question about our sizing options! The key to understanding lumber sizes is in understanding the milling process and exactly what you are purchasing.

Milling Process

When a log reaches a sawmill, it is sawn into specific sizes. Let’s use a 4″ x 8″ timber as an example. At the sawmill the log is milled into a full dimension 4″ thick and 8″ wide piece. Next, we receive that timber here at the Lumber Store yard. When an order is placed for 4″ x 8″, we run it through our mill. Each side of the 4″ x 8″ will get a pass through our bandsaw to remove discolouration and any surface defects. Since the original full dimension 4″ x 8″ has lost some material during our sawing process, the actual sizes of the piece is 3-3/4″ x 7-3/4″. Our bandsaw takes off 1/8″ on each pass.

Nominal vs. Actual Size

When you shop at a local building supply yard for standard construction grade boards, the nominal size is 2″ x 4″ and the actual finished size is 1-1/2″ x 3-1/2″. This is because the wood is kiln dried (wood shrinks during this process) and surfaced on four sides (S4S) and the edges (corners) are slightly rounded (referred to as “eased edge” or EE). The S4SEE process takes off material on each side of the board to end at 1-1/2″ x 3-1/2 S4SEE. We use the nominal sizes (example 2″ x 4″) when quoting projects, but we will always note the actual finished size of the pieces. When we quote 2″ x 4″ Yellow Cedar decking, the same principles apply, we are showing 2″ x 4″ S4SEE Kiln Dried and the actual size is 1-1/2″ x 3-1/2″ that you receive for your project. Where it gets confusing is we also sell 2×4 for projects, that can be bandsawn and green (wet). In this case the finish size is 1-3/4″ x 3-3/4″ as we bandsaw to a smaller size to have a nice finish on the pieces. The more details you provide us about your project, the better we can help you get exactly what you need!


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