Lumber Size Guide

Understand nominal vs actual dimensions, calculate board feet, and find the right lumber sizes for your project. This guide covers every standard size you will encounter in new and reclaimed lumber.

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Why Lumber Sizes Are Confusing

If you have ever picked up a "2x4" and measured it, you already know the number on the label does not match the number on the tape measure. A standard 2x4 actually measures 1.5 inches by 3.5 inches. This discrepancy exists because lumber dimensions are described using nominal sizes — the rough-cut measurement before the wood is dried and planed smooth.

After kiln drying and surfacing, each board loses roughly half an inch in each dimension under 2 inches, and three-quarters of an inch in dimensions 8 inches and above. Understanding this difference is essential for accurate project planning, whether you are framing a wall, building furniture, or specifying reclaimed timbers.

Key rule of thumb: For dimensions under 2", subtract 1/4". For dimensions from 2" to 6", subtract 1/2". For dimensions 8" and above, subtract 3/4".

Standard Dimensional Lumber Sizes

The table below lists every common nominal lumber size alongside its actual finished dimension. These measurements apply to surfaced (S4S) lumber that has been kiln dried. Reclaimed lumber may vary slightly depending on its original milling and how much material is removed during re-surfacing.

Boards (Thickness Under 2")

Nominal Size	Actual Size (inches)	Actual Size (mm)	Common Uses
1 x 2	3/4" x 1-1/2"	19 x 38	Furring strips, lattice, trim
1 x 3	3/4" x 2-1/2"	19 x 64	Trim, battens, craft projects
1 x 4	3/4" x 3-1/2"	19 x 89	Shelving, trim, paneling
1 x 6	3/4" x 5-1/2"	19 x 140	Fencing, shelving, siding
1 x 8	3/4" x 7-1/4"	19 x 184	Shelving, sheathing, paneling
1 x 10	3/4" x 9-1/4"	19 x 235	Shelving, wide trim, paneling
1 x 12	3/4" x 11-1/4"	19 x 286	Wide shelving, cabinet sides

Dimension Lumber (2" Nominal Thickness)

Nominal Size	Actual Size (inches)	Actual Size (mm)	Common Uses
2 x 2	1-1/2" x 1-1/2"	38 x 38	Balusters, light framing, stakes
2 x 3	1-1/2" x 2-1/2"	38 x 64	Furring, light framing, studs
2 x 4	1-1/2" x 3-1/2"	38 x 89	Wall framing, studs, blocking
2 x 6	1-1/2" x 5-1/2"	38 x 140	Floor joists, rafters, decking
2 x 8	1-1/2" x 7-1/4"	38 x 184	Floor joists, rafters, headers
2 x 10	1-1/2" x 9-1/4"	38 x 235	Floor joists, headers, beams
2 x 12	1-1/2" x 11-1/4"	38 x 286	Floor joists, stair stringers, headers

Timbers and Posts (4"+ Nominal)

Nominal Size	Actual Size (inches)	Actual Size (mm)	Common Uses
4 x 4	3-1/2" x 3-1/2"	89 x 89	Posts, columns, railing posts
4 x 6	3-1/2" x 5-1/2"	89 x 140	Posts, beams, headers
4 x 8	3-1/2" x 7-1/4"	89 x 184	Beams, headers, timber framing
4 x 10	3-1/2" x 9-1/4"	89 x 235	Beams, headers, girders
4 x 12	3-1/2" x 11-1/4"	89 x 286	Heavy beams, girders
6 x 6	5-1/2" x 5-1/2"	140 x 140	Heavy posts, timber framing, columns
6 x 8	5-1/2" x 7-1/2"	140 x 190	Heavy beams, timber framing
6 x 10	5-1/2" x 9-1/2"	140 x 241	Heavy beams, bridge timbers
6 x 12	5-1/2" x 11-1/2"	140 x 292	Heavy structural beams
8 x 8	7-1/2" x 7-1/2"	190 x 190	Large posts, columns, timber framing

Board Feet Calculation

A board foot is the standard unit of measure for lumber volume in the United States. One board foot equals a piece of wood 12 inches long, 12 inches wide, and 1 inch thick — or 144 cubic inches of wood.

Board Feet Formula: (Thickness in inches x Width in inches x Length in feet) / 12

Board Feet Examples

Lumber Size	Length	Calculation	Board Feet
2 x 4	8 ft	(2 x 4 x 8) / 12	5.33 BF
2 x 6	10 ft	(2 x 6 x 10) / 12	10.0 BF
2 x 8	12 ft	(2 x 8 x 12) / 12	16.0 BF
2 x 10	16 ft	(2 x 10 x 16) / 12	26.67 BF
2 x 12	8 ft	(2 x 12 x 8) / 12	16.0 BF
4 x 4	8 ft	(4 x 4 x 8) / 12	10.67 BF
6 x 6	10 ft	(6 x 6 x 10) / 12	30.0 BF
1 x 6	8 ft	(1 x 6 x 8) / 12	4.0 BF

Important note: Board feet are calculated using nominal dimensions, not actual dimensions. A 2x4 is calculated as 2 inches x 4 inches regardless of the actual 1.5" x 3.5" measurement. This is the industry standard convention.

For reclaimed lumber that comes in non-standard dimensions, measure the actual thickness and width and use those numbers in the formula. Our team at CA Lumber Recycling can help you calculate board feet for custom-milled reclaimed stock.

Standard Lumber Lengths

Dimensional lumber is commonly sold in even 2-foot increments. Availability may vary depending on species, grade, and whether the lumber is new or reclaimed.

Standard Length	Metric Equivalent	Availability Notes
6 ft	1.83 m	Common in studs and short framing
8 ft	2.44 m	Most common residential framing length
10 ft	3.05 m	Widely available in all sizes
12 ft	3.66 m	Standard for joists and rafters
14 ft	4.27 m	Common for larger structural members
16 ft	4.88 m	Maximum common stocked length
18 ft	5.49 m	Special order in most species
20 ft	6.10 m	Limited availability, higher cost
24 ft	7.32 m	Rare, typically special order only

Reclaimed lumber lengths: Salvaged material often comes in non-standard lengths. At CA Lumber Recycling, we stock reclaimed boards and timbers in a wide range of lengths and can cross-cut to your specifications.

Metric Conversion Reference

While the U.S. lumber industry uses imperial measurements, many international and architectural projects require metric. Use this reference for quick conversions.

Length Conversions

1 inch = 25.4 mm
1 foot = 304.8 mm = 0.3048 m
1 yard = 914.4 mm = 0.9144 m
1 board foot = 2,359.7 cm³

Quick Fraction Reference

1/4" = 6.35 mm
1/2" = 12.7 mm
3/4" = 19.05 mm
1-1/2" = 38.1 mm
3-1/2" = 88.9 mm
5-1/2" = 139.7 mm
7-1/4" = 184.15 mm
9-1/4" = 234.95 mm
11-1/4" = 285.75 mm

Reclaimed Lumber Sizing Considerations

Reclaimed lumber often deviates from modern nominal standards. Older lumber — particularly material from pre-1960 structures — was frequently closer to its nominal size. A reclaimed 2x4 from a 1920s barn may measure a true 2" x 4" or close to it, providing more material than a modern equivalent.

Pre-1900 Lumber

Often full-dimension or very close to nominal. May have rough surfaces on one or more faces. Highly prized for authentic restoration work.

Full Dimension

1900-1960 Lumber

Slightly smaller than full nominal but larger than modern standards. Typical 2x4 may measure 1-5/8" x 3-5/8".

Near Nominal

Post-1960 Lumber

Follows modern standards. A 2x4 measures 1-1/2" x 3-1/2". This is the standard you will find in most new lumber yards.

Modern Standard

Hardwood vs Softwood Dimensional Conventions

Softwoods like Douglas Fir, pine, and spruce follow the nominal-vs-actual sizing convention described above. Hardwoods, however, use an entirely different sizing system based on quarter-inch increments. Hardwood lumber is sold in random widths and lengths, with thickness expressed in quarters of an inch.

Hardwood Thickness (Quarter System)

Quarter Notation	Rough Thickness	S2S (Surfaced 2 Sides)	Common Use
4/4 (four quarter)	1"	13/16" (or 7/8")	Furniture parts, cabinet doors, drawers
5/4 (five quarter)	1-1/4"	1-1/16"	Stair treads, thick tabletops, deck boards
6/4 (six quarter)	1-1/2"	1-5/16"	Workbench tops, bench seats, thick rails
8/4 (eight quarter)	2"	1-3/4"	Table legs, thick aprons, turning blanks
10/4	2-1/2"	2-1/4"	Heavy table legs, mantels
12/4	3"	2-3/4"	Heavy timber furniture, large turning
16/4	4"	3-3/4"	Carving blanks, structural hardwood

Why the difference? Hardwood lumber is sold by the board foot from random-width stock that has been air dried or kiln dried then surfaced to a target thickness. Softwoods are sold by piece count in fixed nominal sizes because they are primarily used in standardized framing layouts. The two systems reflect the different ways each material is consumed.

Decking Lumber Dimensions

Decking material is a special category of dimensional lumber. Unlike standard 2x stock, decking is milled with rounded edges and a slightly thinner profile to accommodate fastening and provide a comfortable walking surface.

Decking Profile	Actual Size (inches)	Edge Profile	Notes
5/4 x 6 Radius Edge	1" x 5-1/2"	Rounded	Most common premium decking
5/4 x 6 Square Edge	1" x 5-1/2"	Square	For grooved hidden fastener systems
2 x 4 Decking	1-1/2" x 3-1/2"	Rounded	Narrow boards, traditional ranch decks
2 x 6 Decking	1-1/2" x 5-1/2"	Rounded	Standard heavy decking, longer spans
1 x 4 T&G	3/4" x 3-1/4" face	Tongue & Groove	Porch flooring, covered surfaces only
1 x 6 T&G	3/4" x 5-1/4" face	Tongue & Groove	Porch flooring, ceiling planks

Reclaimed Beam & Heavy Timber Dimensions

Reclaimed timbers from older industrial buildings, mills, warehouses, and barns frequently come in dimensions that are no longer commercially produced. These oversized members were common before the consolidation of the lumber industry and the shift to engineered wood products.

Reclaimed Timber Size	Approximate Actual	Common Source	Typical Length Range
8 x 8 Douglas Fir	7-1/2" x 7-1/2"	Warehouses, factories	10 to 24 ft
10 x 10 Douglas Fir	9-1/2" x 9-1/2"	Mill buildings, breweries	12 to 28 ft
10 x 12 Heart Pine	9-1/2" x 11-1/2"	Southern textile mills	12 to 30 ft
12 x 12 Oak	11-1/2" x 11-1/2"	Bridge timbers, foundries	14 to 32 ft
12 x 14 Douglas Fir	11-1/2" x 13-1/2"	Heavy industrial floors	16 to 36 ft
14 x 14 Oak	13-1/2" x 13-1/2"	Trestle bridges, mills	16 to 40 ft
16 x 16 Pine/Fir	15-1/2" x 15-1/2"	Major industrial	20 to 48 ft
6 x 12 Doug Fir Joist	5-1/2" x 11-1/2"	Heavy mill flooring	14 to 24 ft
3 x 12 Doug Fir Decking	2-1/2" x 11-1/4"	Mill deck, bridge decking	10 to 24 ft

When working with reclaimed timbers, plan on losing 1/4" to 3/4" from each face if you intend to re-surface the wood. Many designers prefer to leave the original surfaces intact to preserve patina, original saw marks, and visible signs of the wood's history.

Regional and Historic Sizing Variations

Lumber dimensions have not always been standardized. Before the establishment of the American Lumber Standards Committee (ALSC) in 1924, every region — and often every mill — used its own dimensional conventions. These variations show up regularly in reclaimed material from older structures.

New England (Pre-1900)

Pine and Eastern hemlock sawn at full nominal dimensions. Eastern White Pine boards commonly 18 to 24 inches wide. Hand-hewn timbers from Colonial-era barns measure close to nominal but with adze marks on faces.

Pacific Northwest (1880-1940)

Old-growth Douglas Fir and Redwood sawn slightly oversize to allow for finishing. A 2x6 of this era often measures 1-3/4" x 5-3/4". Beam stock could be massive — single 16x16 timbers up to 60 ft long.

Southern States (1850-1930)

Heart Pine and Cypress milled at near-nominal dimensions in fixed lengths. Mill-floor stock 3" or 4" thick was common. Wide flooring boards 8 to 14 inches wide were standard in plantation homes.

Midwest (1860-1920)

Oak, ash, and elm sawn for barn timbers in dimensions tied to local building traditions. Common timber sizes included 8x8, 10x10, and 12x12 in lengths up to 30 ft. Pegged mortise-and-tenon joinery preserved through reclaim.

California Mission Era

Hand-adzed Redwood and Sugar Pine timbers in non-standard dimensions reflecting Spanish colonial measurement traditions. Vigas (round log beams) and corbels typical of adobe construction.

Modern Standardized (Post-1964)

The 1964 American Softwood Lumber Standard finalized current nominal-vs-actual conventions. All commercial lumber from this era forward uses the dimensions in the tables above, regardless of region.

Specialty Lumber Profiles

Beyond the standard dimensional and board categories, the lumber industry produces dozens of specialty profiles for specific applications. These are often the cuts you encounter when working with reclaimed material from particular historical sources.

Profile Name	Typical Size	Description & Use
Bevel Siding	1/2" x 6" tapered	Tapered horizontal siding, lap installation
Channel Siding	1" x 8" rabbeted	Overlapping channel rabbet, board-and-batten substitute
Shiplap	3/4" x 5-1/2" face	Interlocking rabbet edges, popular for accent walls
V-Groove T&G	3/4" x 3-1/4" face	Tongue and groove with V-bevel, paneling
Beadboard	3/8" or 1/2"	T&G with bead detail, traditional wainscot
Lath	1/4" x 1-1/2"	Thin strips for plaster substrate, garden trellis
Battens	3/4" x 2" or 3"	Cover strips for board-and-batten siding
Furring	3/4" x 1-1/2"	Spacers under finish material over masonry
Mill Decking	2" or 3" T&G	Heavy industrial floor planks, mill construction
Stair Tread	1-1/16" x 11-1/2"	Bull-nosed front edge, glue-laminated common

Practical Quantity Calculations

Converting between board feet, linear feet, and square feet is one of the most common tasks in lumber estimating. Each unit measures something different and the conversion depends on the actual dimensions of your material.

Linear Feet to Board Feet

Multiply linear feet by the nominal cross-section in inches, then divide by 12. For 100 linear feet of 2x6: (100 x 2 x 6) / 12 = 100 BF.

Square Feet to Board Feet

For nominal 1" thick stock, square feet equal board feet. For 5/4 hardwood, multiply square feet by 1.25. For 8/4, multiply by 2.0.

Coverage Area for Flooring

T&G flooring face width is less than nominal width. A nominal 4" T&G board has 3-1/4" face. Calculate coverage using face width, not nominal.

Waste Allowance

Add 10% waste for square rooms, 15% for irregular layouts, 20% for diagonal or herringbone patterns. Reclaimed lumber typically needs 15-20% extra for cull and trim.

Detailed Size Guides

Explore our specialized guides for more detailed sizing information.

Guide

Dimensional Lumber Guide

Deep dive into every standard dimensional lumber size — studs, joists, rafters, beams, and more. Includes span tables and load-bearing specifications.