Lumber Dimensions Chart: Nominal vs Actual Sizes

Lumber Dimensions: Nominal vs Actual Size

When you buy a "2x4" at the lumber yard, it does not actually measure 2 inches by 4 inches. Lumber is sold by its nominal size (the rough-cut size before drying and planing), but the actual size is smaller after the wood is dried and surfaced. This chart shows the actual dimensions you will receive for every common lumber size.

Softwood Lumber Dimensions (Pine, Spruce, Fir, Cedar)

Nominal Size	Actual Size (inches)	Actual Size (mm)	Common Use
1 × 2	3/4 × 1-1/2	19 × 38	Furring strips, craft projects
1 × 3	3/4 × 2-1/2	19 × 64	Furring strips, trim
1 × 4	3/4 × 3-1/2	19 × 89	Trim, shelving, craft
1 × 6	3/4 × 5-1/2	19 × 140	Shelving, fence boards, paneling
1 × 8	3/4 × 7-1/4	19 × 184	Shelving, sheathing
1 × 10	3/4 × 9-1/4	19 × 235	Wide shelving, cabinetry
1 × 12	3/4 × 11-1/4	19 × 286	Wide shelving, cabinetry
2 × 2	1-1/2 × 1-1/2	38 × 38	Balusters, light framing
2 × 3	1-1/2 × 2-1/2	38 × 64	Light framing, furring
2 × 4	1-1/2 × 3-1/2	38 × 89	Wall studs, general framing
2 × 6	1-1/2 × 5-1/2	38 × 140	Exterior walls, floor joists, deck boards
2 × 8	1-1/2 × 7-1/4	38 × 184	Floor joists, rafters, headers
2 × 10	1-1/2 × 9-1/4	38 × 235	Floor joists, rafters, stair stringers
2 × 12	1-1/2 × 11-1/4	38 × 286	Floor joists, ridge beams, stair stringers
4 × 4	3-1/2 × 3-1/2	89 × 89	Fence posts, deck posts, columns
4 × 6	3-1/2 × 5-1/2	89 × 140	Beams, posts, structural supports
6 × 6	5-1/2 × 5-1/2	140 × 140	Heavy posts, timber framing
6 × 8	5-1/2 × 7-1/2	140 × 190	Beams, heavy timber
8 × 8	7-1/2 × 7-1/2	190 × 190	Heavy beams, commercial construction

Hardwood Lumber Dimensions (Oak, Maple, Cherry, Walnut)

Hardwood is sold by the "quarter" system, referring to the rough-sawn thickness in quarter-inches. After surfacing (S2S = surfaced two sides), the actual thickness is reduced.

Quarter Designation	Rough Thickness	Surfaced (S2S) Thickness	Common Name
4/4 (four-quarter)	1"	13/16" (0.8125")	One-inch stock
5/4 (five-quarter)	1-1/4"	1-1/16" (1.0625")	Deck boards, heavy shelving
6/4 (six-quarter)	1-1/2"	1-5/16" (1.3125")	Table tops, thick stock
8/4 (eight-quarter)	2"	1-13/16" (1.8125")	Table legs, thick stock
10/4 (ten-quarter)	2-1/2"	2-5/16" (2.3125")	Heavy timber, turning blanks
12/4 (twelve-quarter)	3"	2-13/16" (2.8125")	Heavy beams, large turning
16/4 (sixteen-quarter)	4"	3-13/16" (3.8125")	Heavy structural, carving blocks

Board Feet Calculation

Lumber is priced by the board foot, a unit of volume equal to a 1-inch thick board that is 12 inches wide and 12 inches long (144 cubic inches).

Board Feet = (Thickness in inches × Width in inches × Length in feet) ÷ 12

Board Size	Length 8 ft	Length 10 ft	Length 12 ft	Length 16 ft
1 × 4	2.67 bf	3.33 bf	4.00 bf	5.33 bf
1 × 6	4.00 bf	5.00 bf	6.00 bf	8.00 bf
1 × 8	5.33 bf	6.67 bf	8.00 bf	10.67 bf
1 × 12	8.00 bf	10.00 bf	12.00 bf	16.00 bf
2 × 4	5.33 bf	6.67 bf	8.00 bf	10.67 bf
2 × 6	8.00 bf	10.00 bf	12.00 bf	16.00 bf
2 × 8	10.67 bf	13.33 bf	16.00 bf	21.33 bf
2 × 10	13.33 bf	16.67 bf	20.00 bf	26.67 bf
2 × 12	16.00 bf	20.00 bf	24.00 bf	32.00 bf
4 × 4	10.67 bf	13.33 bf	16.00 bf	21.33 bf
6 × 6	24.00 bf	30.00 bf	36.00 bf	48.00 bf

Standard Lumber Lengths

Softwood dimensional lumber is available in standard lengths of 8, 10, 12, 14, 16, 18, 20, 22, and 24 feet. The most commonly stocked lengths at home centers are 8, 10, 12, and 16 feet. Longer lengths may need to be special ordered.

Pressure-Treated Lumber Notes

• Pressure-treated lumber has the same nominal and actual dimensions as untreated lumber.
• Treated lumber will shrink slightly as it dries after purchase (it is sold wet).
• Common treatment chemicals include ACQ (Alkaline Copper Quaternary) and CA-C (Copper Azole).
• Use treated lumber for any ground contact, outdoor, or moisture-exposed applications.
• Always use stainless steel or coated fasteners with pressure-treated lumber.