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Wood Sizing

Wood Sizing

The size given for any particular piece of wood is the dimension the wood had in its rough state. The process of surfacing the wood removes a certain amount of wood from the board, and therefore the final dimension will always be smaller than the original. The following table shows the rough dimension, and the actual dimension of the final surfaced piece.

Softwood Dimensional Lumber Sizes
NominalActualNominalActual
1 × 2¾″ × 1½″ (19×38 mm)2 × 21½″ × 1½″ (38×38 mm)
1 × 3¾″ × 2½″ (19×64 mm)2 × 31½″ × 2½″ (38×64 mm)
1 × 4¾″ × 3½″ (19×89 mm)2 × 41½″ × 3½″ (38×89 mm)
1 × 6¾″ × 5½″ (19×140 mm)                 2 × 61½″ × 5½″ (38×140 mm)                 
1 × 8¾″ × 7¼″ (19×184 mm)                 2 × 81½″ × 7¼″ (38×184 mm)                 
1 × 10¾″ × 9¼″ (19×235 mm)                 2 × 101½″ × 9¼″ (38×235 mm)                 
1 × 12¾″ × 11¼″ (19×286 mm)                  2 × 121½″ × 11¼″ (38×286 mm)                  
3 × 42½″ × 3½″ (64×89 mm)                 2 × 141½″ × 13¼″ (38×337 mm)                  
4 × 43½″ × 3½″ (89×89 mm)                 6 × 65½″ × 5½″ (140×140 mm)                  
4 × 63½″ × 5½″ (89×140 mm)                  8 × 87¼″ × 7¼″ (184×184 mm)                  

In North America, hardwood lumber is often referred to using the "quarter" system. 4/4 would refer to a 1-inch thick piece of wood, while 5/4 would refer to a 1 1/4-inch piece of wood.

Hardwood Dimensional Lumber Sizes
Nominal                 Surfaced 1 Side (S1S)                  Surfaced 2 sides (S2S)                  
?″¼″3/16″ (4.8 mm)
½″?″5/16″ (7.9 mm)
?″½″7/16″ (9.4 mm)
¾″?″9/16″ (14.3 mm)
1″ or 4/4?″13/16″ (20.6 mm)
1¼″ or 5/4                  1?″1-1/16″ (20.7 mm)
1½″ or 6/4                  1?″1-5/16″ (33.3 mm)
2″ or 8/41-13/16″1¾″ (44.4 mm)
3″ or 12/4                 2-13/16″2¾″ (69.8 mm)
4″ or 16/4                 3-13/16″3¾″ (95.2 mm)

North American hardwood lumber is commonly sold by unit of board-foot (144 cubic inches). This equates to a piece of wood 1 inch thick, 12 inches wide, and 12 inches long (all sizes nominal/rough).

In regions outside of North America, lumber sizes are represented differently. Some regions use imperial measurements (inches, feet) and other regions use metric lengths.

Examples of Dimensional Lumber Sizes (Softwood and Hardwood)                  
Inch nameSawedSwedishAustralian
2 × 450 x 100 mm45 × 95 mm45 x 90 mm
1 × 325 × 75 mm22 × 70 mm19 x 70 mm
3 × 375 × 75 mm70 × 70 mm70 x 70 mm
2 × 750 × 175 mm45 × 170 mmNot used
2 × 350 × 75 mm45 × 70 mm45 x 70 mm
1 × 425 × 100 mm22 × 95 mm19 x 90 mm
1 × 525 × 125 mm22 × 120 mm19 x 120 mm
2 × 550 × 125 mm45 × 120 mm45 x 120 mm

Since the type of finishing affects the final thickness, please note that the table below shows the thickness for surfaced two sides (S2S) wood. Also note that surfaced hardwood and surfaced softwood differ slightly.

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