In lumber, nominal size and actual size refer to different ways of describing the same piece of wood. These refer to the thickness and width of the wood, with the length varying.
Nominal Size (or trade size): the rough cut size of the lumber before it is planed and finished. It’s how big the wood is originally cut at the sawmill before drying and milling.
Actual Size (or dimensional size): the true, final size of the lumber after it has been dried and surfaced on all four sides. This is the actual measurement we receive from our vendors if we used a tape measure, and explains why our cornices come out to be 9.25” wide even when customers order for 10”.
When nominal lumber is processed in the mill, it goes through a dehydration process to reduce the moisture content, causing shrinkage. It then goes through the planing or surfacing process on all 4 sides to smooth the board out before being ready for sale.
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