Lumber Tally field notes
Lumber Thickness: Nominal Sizes and the Quarter System
What 4/4 and a 2x4 actually mean, why the number on the price list is rarely the number your calipers show, and why that is not a defect.
The thickness written on a price list, a tally sheet, or a board's end tag is almost always a nominal size — a trade name for the board, not a promise about what a caliper will read. Two different naming systems cover this in North America: dimensional (softwood construction lumber) and the quarter system (hardwood).
Softwood: nominal vs. actual
A construction "2×4" starts life close to 2 by 4 inches rough, but drying and planing remove material before it reaches the yard. The American Softwood Lumber Standard, PS 20-20 sets the minimum dressed sizes; a nominal 2×4 finishes at 1½ × 3½ inches, and a nominal 1×6 finishes at ¾ × 5½ inches (Archtoolbox).
| Nominal | Actual (dressed) |
|---|---|
| 1 × 4 | ¾ × 3½ in |
| 1 × 6 | ¾ × 5½ in |
| 2 × 4 | 1½ × 3½ in |
| 2 × 6 | 1½ × 5½ in |
| 2 × 8 | 1½ × 7¼ in |
| 4 × 4 | 3½ × 3½ in |
Hardwood: the quarter system
Hardwood is thickness-graded in quarters of an inch: 4/4 ("four-quarter") is nominally 1 inch, 8/4 is 2 inches, 12/4 is 3 inches. This number is the rough thickness the board is graded and typically priced at — it is not the thickness you get after surfacing:
| Nominal | Rough | Surfaced 2 sides (S2S) |
|---|---|---|
| 4/4 | 1 in | ≈ 13/16 in |
| 5/4 | 1¼ in | ≈ 1 1/16 in |
| 6/4 | 1½ in | ≈ 1 5/16 in |
| 8/4 | 2 in | ≈ 1¾ in |
| 12/4 | 3 in | ≈ 2¾ in |
| 16/4 | 4 in | ≈ 3¾ in |
Even that S2S column is a typical figure, not a guarantee: grading rules allow a range, actual planer output varies by mill and species, and there is no single industry-wide number for "actual" surfaced thickness (WoodBin, citing wood scientist Gene Wengert). A 4/4 board might come off the planer at 13/16 inch, 15/16 inch, or somewhere between, depending on how much material the mill and your own jointing removed (Woodworking Network).
What this means for a tally
Typing 4/4 gives the calculator a thickness of 1 inch.
That may be appropriate when your supplier bills nominal rough thickness.
For the physical volume of a finished board, enter its measured thickness
instead. Confirm the supplier's billing dimensions and rounding rules
before comparing your tally with an invoice. This calculator measures
rectangular boards; it does not apply log-scaling rules such as Doyle or
Scribner to estimate the lumber yield of a log.
Next: rough vs. finished lumber covers why that gap between nominal and actual exists in more detail. Back to the calculator.
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