Lumber Waste Calculator — Nominal vs Actual Size
A 1×6 is not 6 inches wide. It is 5½. A 2×4 is not 2 by 4 — it is 1½ by 3½. Coverage calculators built on nominal sizes undercount boards by 8 to 9 percent. This one shows both answers side by side.
Results
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Questions people ask
What is the actual size of a 1x6 board?
A nominal 1×6 is milled to ¾ inch thick by 5½ inches wide. The 6 inch figure refers to the rough-sawn width before drying and planing, and is the historical basis for pricing.
Is 4/4 lumber really 1 inch thick?
No. 4/4 is rough-sawn at 1 inch and is normally surfaced down to 13/16 inch, sometimes 3/4. It is still sold and billed as 4/4, which is why board foot conversion uses 1 inch as the nominal thickness.
How many boards do I need for 320 square feet of 1x6 siding?
At 5½ inch actual coverage you need 88 boards for 8 foot lengths. Calculated from the nominal 6 inch width it returns 80 — eight boards short, or 48 linear feet you will have to buy twice.
Does this apply to 2x4 framing lumber too?
Yes. A 2×4 is 1½ × 3½ inches. When you lay 2×4 flat as decking, the 3½ inch width is what covers the area, not 4 inches. For framing with joist hangers, the 1½ inch thickness is what sets the floor height.
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