Why a 2×4 is really 1½″ × 3½″ — lookup tables for softwood dimensional, hardwood rough-sawn, and plywood.
Dimensional lumber is sold by nominal size but delivered at a smaller actual size — the result of drying and surfacing (S4S) at the mill.
| Nominal | Actual thickness | Actual width | Actual area |
|---|---|---|---|
| 1×2 | 3/4" | 1-1/2" | 1.125 sq in |
| 1×3 | 3/4" | 2-1/2" | 1.875 sq in |
| 1×4 | 3/4" | 3-1/2" | 2.625 sq in |
| 1×6 | 3/4" | 5-1/2" | 4.125 sq in |
| 1×8 | 3/4" | 7-1/4" | 5.438 sq in |
| 1×10 | 3/4" | 9-1/4" | 6.938 sq in |
| 1×12 | 3/4" | 11-1/4" | 8.438 sq in |
| 2×2 | 1-1/2" | 1-1/2" | 2.250 sq in |
| 2×3 | 1-1/2" | 2-1/2" | 3.750 sq in |
| 2×4 | 1-1/2" | 3-1/2" | 5.250 sq in |
| 2×6 | 1-1/2" | 5-1/2" | 8.250 sq in |
| 2×8 | 1-1/2" | 7-1/4" | 10.875 sq in |
| 2×10 | 1-1/2" | 9-1/4" | 13.875 sq in |
| 2×12 | 1-1/2" | 11-1/4" | 16.875 sq in |
| 3×4 | 2-1/2" | 3-1/2" | 8.750 sq in |
| 3×6 | 2-1/2" | 5-1/2" | 13.750 sq in |
| 4×4 | 3-1/2" | 3-1/2" | 12.250 sq in |
| 4×6 | 3-1/2" | 5-1/2" | 19.250 sq in |
| 4×8 | 3-1/2" | 7-1/4" | 25.375 sq in |
| 6×6 | 5-1/2" | 5-1/2" | 30.250 sq in |
| 6×8 | 5-1/2" | 7-1/2" | 41.250 sq in |
| 8×8 | 7-1/2" | 7-1/2" | 56.250 sq in |
Hardwoods are sold by the quarter — each quarter equals ¼″. So 4/4 = 1 nominal inch. "Rough" means as-sawn; S2S means surfaced two sides (top & bottom).
| Quarter designation | Nominal thickness | Rough actual | S2S (surfaced) | Common use |
|---|---|---|---|---|
| 4/4 | 1" | 1" | 13/16" | Standard furniture stock |
| 5/4 | 1-1/4" | 1-1/4" | 1-1/16" | Table tops, wide panels |
| 6/4 | 1-1/2" | 1-1/2" | 1-5/16" | Heavier furniture parts |
| 8/4 | 2" | 2" | 1-3/4" | Legs, turning blanks |
| 10/4 | 2-1/2" | 2-1/2" | 2-1/4" | Heavy legs, slabs |
| 12/4 | 3" | 3" | 2-3/4" | Large turning blanks |
| 16/4 | 4" | 4" | 3-3/4" | Thick slabs, large workpieces |
S2S thickness assumes a light skim pass. Many hardwood dealers sell S2S at 3/16″ less than rough for 4/4–6/4, and 1/4″ less for thicker stock.
Plywood sheets are typically 1/32″ undersize. This matters most for dadoes and grooves — a "¾″ dado" will be too loose for a 23/32″ sheet.
| Nominal | Listed thickness | Actual thickness | Best for |
|---|---|---|---|
| 1/4" | 1/4" | 7/32" (0.219") | Back panels, drawer bottoms |
| 3/8" | 3/8" | 11/32" (0.344") | Lightweight panels |
| 1/2" | 1/2" | 15/32" (0.469") | Shelves, cabinet boxes (lighter) |
| 5/8" | 5/8" | 19/32" (0.594") | Shelves, subflooring |
| 3/4" | 3/4" | 23/32" (0.719") | Cabinet boxes, countertops — most common |
| 1" | 1" | 31/32" (0.969") | Heavy shelves, workbench tops |
Softwood dimensional lumber is sized when freshly cut ("green"). Drying and surfacing (planing all four sides, S4S) removes roughly ¼″–½″ from each face, shrinking a nominal 2×4 from 2″×4″ down to the actual 1½″×3½″ we buy today. These actual sizes were standardised in the 1960s.
Hardwoods are sold rough (as-sawn) or surfaced on two sides (S2S). Because the customer often does their own final surfacing, a small amount of material is left for clean-up — hence 4/4 rough stock (nominally 1″) typically surfaces to 13/16″ after S2S.