Lumber Tally field notes
Rough vs. Finished Lumber
How surfacing changes lumber dimensions, and how to choose between measured dimensions and supplier billing dimensions.
Lumber exists in at least two states between the sawmill and your project: rough-sawn, as it comes off the saw with visible saw marks and an uneven surface, and surfaced (planed smooth), which removes material to leave flat, parallel faces. The distinction matters directly for board-foot math, because the two states are not the same size.
Surfacing removes wood
"S1S" means surfaced one side, "S2S" surfaced two sides, "S4S" surfaced four sides (both faces and both edges). Each pass takes material off:
| Rough | S1S | S2S |
|---|---|---|
| 1 in (4/4) | ≈ 7/8 in | ≈ 13/16 in |
| 1½ in (6/4) | ≈ 1 3/8 in | ≈ 1 5/16 in |
| 2 in (8/4) | ≈ 1 13/16 in | ≈ 1¾ in |
Which size do you price with?
For a buying estimate, use the dimensions your supplier bills. For example, Parkerville Wood Products instructs customers to "use this calculator with rough lumber dimensions only." A physical-volume calculation for a finished board instead uses the finished measurements. This tool makes neither choice for you: it calculates from the dimensions you enter without silently changing them.
Why it is not exact
How much a given board loses to the planer is not fixed. It depends on species, how flat the board needs to end up, how much the board has cupped or twisted, and how the mill graded it. Grading rules themselves build in a range rather than one number — for kiln-dried 4/4 lumber, grading allows the thinnest point to run as low as 13/16 inch once surfaced two sides (Woodworking Network). Treat any "actual thickness" figure, including the tables on this site, as typical rather than guaranteed, and confirm against your supplier's invoice when it matters.
See lumber thickness and the quarter system for the full nominal-size tables, or head to the calculator to tally rough dimensions directly.
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