Lumber Sizing Guide
A comprehensive reference for lumber dimensions, board foot calculations, and the unique sizing characteristics of reclaimed wood.
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Nominal vs. Actual Dimensions
One of the most common sources of confusion for anyone buying lumber is the difference between nominal and actual dimensions. When you purchase a "2x4" from a modern lumber yard, the board is not actually 2 inches by 4 inches. It is 1-1/2 inches by 3-1/2 inches.
This discrepancy exists because lumber is named by its rough-sawn size before drying and planing. After the wood is kiln-dried (which causes shrinkage) and surfaced smooth on all four sides (S4S), the finished product is smaller than its nominal designation. These standards were established by the American Lumber Standard Committee and have been in effect since 1964.
Prior to 1964, dimensional standards varied. A "2x4" from the early 1900s might actually measure closer to 1-5/8" x 3-5/8" or even a full 2" x 4" if it was never surfaced. This is important when working with reclaimed lumber from historic structures.
| Nominal Size | Actual Size (inches) | Actual Size (mm) |
|---|---|---|
| 1 x 2 | 3/4" x 1-1/2" | 19 x 38 |
| 1 x 3 | 3/4" x 2-1/2" | 19 x 64 |
| 1 x 4 | 3/4" x 3-1/2" | 19 x 89 |
| 1 x 6 | 3/4" x 5-1/2" | 19 x 140 |
| 1 x 8 | 3/4" x 7-1/4" | 19 x 184 |
| 1 x 10 | 3/4" x 9-1/4" | 19 x 235 |
| 1 x 12 | 3/4" x 11-1/4" | 19 x 286 |
| 2 x 2 | 1-1/2" x 1-1/2" | 38 x 38 |
| 2 x 3 | 1-1/2" x 2-1/2" | 38 x 64 |
| 2 x 4 | 1-1/2" x 3-1/2" | 38 x 89 |
| 2 x 6 | 1-1/2" x 5-1/2" | 38 x 140 |
| 2 x 8 | 1-1/2" x 7-1/4" | 38 x 184 |
| 2 x 10 | 1-1/2" x 9-1/4" | 38 x 235 |
| 2 x 12 | 1-1/2" x 11-1/4" | 38 x 286 |
| 4 x 4 | 3-1/2" x 3-1/2" | 89 x 89 |
| 4 x 6 | 3-1/2" x 5-1/2" | 89 x 140 |
| 6 x 6 | 5-1/2" x 5-1/2" | 140 x 140 |
| 6 x 8 | 5-1/2" x 7-1/2" | 140 x 190 |
| 8 x 8 | 7-1/2" x 7-1/2" | 190 x 190 |
Important Note for Reclaimed Lumber
Reclaimed lumber often does not match modern nominal or actual dimensions precisely. Wood from pre-1900 structures was typically rough-sawn and may be closer to true nominal size, while wood from mid-century buildings might fall somewhere in between. Always measure reclaimed boards individually and plan for variation. At Lumber New Orleans, we provide actual measured dimensions for all our reclaimed stock.
Board Foot Calculations
A board foot (BF) is the standard unit of measure for lumber volume in the United States. One board foot equals a piece of wood that is 1 inch thick, 12 inches wide, and 12 inches long -- or 144 cubic inches of wood.
Board feet are used for pricing hardwoods, reclaimed lumber, and specialty wood. Unlike dimensional lumber sold by the piece, reclaimed wood is almost always priced per board foot, making this calculation essential.
The Board Foot Formula
BF = (T x W x L) / 12
Where T = thickness in inches, W = width in inches, L = length in feet
Thickness (T) is measured in inches. Use the nominal thickness for standard lumber (e.g., use 2 for a 2x4, even though the actual thickness is 1.5 inches). For reclaimed lumber, use the actual measured thickness.
Width (W) is measured in inches. Same rule applies -- nominal for standard lumber, actual for reclaimed.
Length (L) is measured in feet. Boards are typically sold in even-foot lengths.
Board Foot Calculation Examples
One 2x4, 8 feet long
2 x 4 x 8 / 12 = 5.33 BF
One 2x6, 10 feet long
2 x 6 x 10 / 12 = 10 BF
One 2x12, 12 feet long
2 x 12 x 12 / 12 = 24 BF
One 1x6, 8 feet long
1 x 6 x 8 / 12 = 4 BF
One 4x4, 10 feet long
4 x 4 x 10 / 12 = 13.33 BF
One 6x6, 12 feet long
6 x 6 x 12 / 12 = 36 BF
One 1x12, 6 feet long
1 x 12 x 6 / 12 = 6 BF
One 2x8, 14 feet long
2 x 8 x 14 / 12 = 18.67 BF
One 8x8, 16 feet long
8 x 8 x 16 / 12 = 85.33 BF
Ten 2x4s, 8 feet long
10 x (2 x 4 x 8 / 12) = 53.33 BF
Quick Tip: Estimating Costs
To estimate the cost of lumber, multiply the total board feet by the price per board foot. For example, if you need twenty 2x6 boards that are 10 feet long, that is 20 x 10 BF = 200 board feet. At $5 per board foot, the total cost would be $1,000. Reclaimed lumber prices vary significantly based on species, grade, and character -- contact us for current pricing.
Standard Lumber Lengths
Modern lumber is sold in standard even-foot lengths. Reclaimed lumber may come in non-standard lengths depending on the source structure. Longer reclaimed boards are rarer and command a premium.
| Length | Metric | Common Uses |
|---|---|---|
| 8 feet | 2.44 m | Wall studs (for 8-foot ceilings), short framing |
| 10 feet | 3.05 m | General framing, floor joists, headers |
| 12 feet | 3.66 m | Rafters, longer spans, ceiling joists |
| 14 feet | 4.27 m | Floor joists, longer beams |
| 16 feet | 4.88 m | Roof rafters, longer floor spans |
| 18 feet | 5.49 m | Heavy framing, commercial applications |
| 20 feet | 6.10 m | Large-scale framing, structural beams |
| 24 feet | 7.32 m | Specialty applications (usually special order) |
How Reclaimed Lumber Differs
Pre-1900 Rough-Sawn Lumber
Lumber from the 19th century was typically sawn by water- or steam-powered mills and left unsurfaced. These boards are often very close to their nominal dimensions. A "2x10" from an 1880s warehouse might actually measure 2" x 10" or close to it. The surfaces show circular or band-saw marks and may have irregular thickness along the length.
Early 20th Century (1900-1950)
As planing mills became common, lumber from this era was surfaced but to different standards than today. A "2x4" might measure 1-5/8" x 3-5/8" -- slightly larger than modern boards but smaller than true nominal. Widths are more consistent but still vary from board to board.
Post-1964 Standard Lumber
After the American Lumber Standard Committee established uniform rules in 1964, all surfaced (S4S) lumber was milled to the actual dimensions we use today. Reclaimed lumber from buildings built after this date will generally match modern sizing, though decades of service may have caused warping, cupping, or surface wear.
Measuring Tips for Reclaimed Wood
Always measure reclaimed boards at multiple points along their length, as thickness and width can vary. Use calipers for accurate thickness readings. Account for material removal during re-surfacing -- typically 1/16" to 1/8" per face. When planning a project, buy 15-20% more reclaimed lumber than calculated to account for defects, trimming, and waste.
Practical Measuring Tips
Use the Right Tools
- •Use a tape measure for length and width
- •Use dial or digital calipers for precise thickness
- •A moisture meter helps predict final dimensions after drying
- •A straightedge reveals bowing, cupping, and twist
Measure Multiple Points
- •Check thickness at both ends and the center
- •Measure width at several points along the length
- •Note the thinnest dimension -- that is your usable size
- •Mark boards that are significantly out of spec
Plan for Processing
- •Planing removes 1/16" to 1/8" per pass per face
- •Ripping removes 1/8" from the blade kerf
- •Jointing one edge removes roughly 1/16" to 1/8"
- •Account for end-trimming to remove checks and splits
Reclaimed Lumber Sizing by Era
Lumber dimensions have changed dramatically over the past 150 years. Before standardization, sawmills cut lumber to roughly nominal size and often left it unsurfaced. As planing became standard practice in the early 20th century, finished dimensions shrank slightly. The modern standard we know today was not established until 1964 by the American Lumber Standard Committee.
When working with reclaimed lumber, knowing the era of the source building tells you what dimensions to expect. A 2x4 from a Civil War-era warehouse will be measurably larger than one pulled from a 1940s factory, which will in turn be slightly larger than a post-1964 board. This table shows the typical actual dimensions you will encounter at each era.
| Nominal Size | Pre-1900 Rough-sawn, true nominal | 1900 - 1950 Surfaced, pre-standard | 1964+ Modern ALSC standard |
|---|---|---|---|
| 2 x 4 | 2" x 4" | 1-5/8" x 3-5/8" | 1-1/2" x 3-1/2" |
| 2 x 6 | 2" x 6" | 1-5/8" x 5-5/8" | 1-1/2" x 5-1/2" |
| 2 x 8 | 2" x 8" | 1-5/8" x 7-1/2" | 1-1/2" x 7-1/4" |
| 2 x 10 | 2" x 10" | 1-5/8" x 9-1/2" | 1-1/2" x 9-1/4" |
| 2 x 12 | 2" x 12" | 1-5/8" x 11-1/2" | 1-1/2" x 11-1/4" |
| 4 x 4 | 4" x 4" | 3-5/8" x 3-5/8" | 3-1/2" x 3-1/2" |
| 4 x 6 | 4" x 6" | 3-5/8" x 5-5/8" | 3-1/2" x 5-1/2" |
| 6 x 6 | 6" x 6" | 5-5/8" x 5-5/8" | 5-1/2" x 5-1/2" |
| 6 x 8 | 6" x 8" | 5-5/8" x 7-1/2" | 5-1/2" x 7-1/2" |
| 8 x 8 | 8" x 8" | 7-1/2" x 7-1/2" | 7-1/2" x 7-1/2" |
Why This Matters for Your Project
If you are matching reclaimed lumber to existing framing or millwork in a historic building, knowing the era helps you select compatible stock. Pre-1900 lumber often needs to be planed down to fit with modern material, while mid-century lumber may only need minimal adjustment. When mixing eras in a single project, always plan to mill everything to a common dimension -- typically the smallest piece dictates the final size.
Coverage Calculator: How Much Lumber Do You Need?
One of the most common questions we hear is "how much wood do I need?" Below are worked examples for common residential projects. Each example includes a waste factor -- always order more than the bare minimum to account for cutting, defects, and mismatched pieces.
100 sq ft hardwood floor (3/4" thick x 3-1/4" wide planks)
Approx. 100 BF (1:1 ratio for 3/4" thick stock) + 10% waste = 110 BF
Tongue-and-groove flooring has a milling loss of about 25%, so order roughly 133 BF of rough lumber if milling your own.
8 ft wide x 9 ft tall accent wall (1x6 T&G planks, horizontal)
72 sq ft of wall area / 0.458 sq ft per lineal foot of 1x6 = ~157 LF. At 1x6, that is ~79 BF + 15% waste = ~91 BF
Account for staggered end joints and cut-off waste around outlets and switches.
16 ft mantel beam (8" x 8" solid timber)
8 x 8 x 16 / 12 = 85.33 BF
Hollow box-beam alternative uses roughly 30 BF of 1x8 material plus framing.
12 ft x 12 ft deck surface (5/4 x 6 decking)
144 sq ft / 0.458 sq ft per LF of 5/4x6 = ~314 LF. At 5/4x6, that is ~196 BF + 10% waste = ~216 BF
Use rot-resistant species like cypress. Add joists and framing lumber separately.
10 LF of kitchen open shelving (3 shelves, 1x10)
3 x (1 x 10 x 10 / 12) = 25 BF + bracket/cleat material
Heart pine or white oak recommended for heavy loads. Account for finishes.
Barn-door build (36" x 84", 1x6 planks + Z-brace)
Face boards: ~21 sq ft = ~21 BF. Z-brace: ~8 BF. Total: ~29 BF + 10% = ~32 BF
Choose a dimensionally stable species. Kiln-dried recommended to prevent warping.
Linear Feet vs. Board Feet vs. Square Feet
These three units measure different things, and confusing them is one of the most common mistakes when ordering lumber. Here is what each one means, how to convert between them, and when each measurement is used.
Linear Feet (LF)
A simple length measurement -- one linear foot is 12 inches, regardless of width or thickness. Used when buying trim, molding, decking, and fencing where the profile is already defined. If you buy 100 LF of 1x6 deck boards, you are getting 100 feet of board, each one 1 inch thick and 6 inches wide.
Formula
LF = total length in feet
Board Feet (BF)
A unit of volume. One board foot equals a piece of wood 1" thick x 12" wide x 12" long (144 cubic inches). Used for pricing hardwood lumber, reclaimed wood, and specialty material. Board feet account for thickness and width, so a thicker or wider board costs proportionally more per linear foot.
Formula
BF = (T" x W" x L') / 12
Square Feet (SF)
An area measurement. One square foot is a 12" x 12" area. Used for flooring, wall paneling, decking coverage, and roofing. Square footage tells you how much surface area the lumber will cover but does not account for thickness -- a 3/4" thick floor and a 1-1/2" thick floor cover the same square footage but use very different amounts of wood.
Formula
SF = (W" x L') / 12
Conversion Formulas & Examples
| Conversion | Formula | Example |
|---|---|---|
| Linear Feet to Board Feet | LF x (T" x W") / 12 = BF | 20 LF of 2x6: 20 x (2 x 6) / 12 = 20 BF |
| Board Feet to Linear Feet | BF x 12 / (T" x W") = LF | 50 BF of 2x6: 50 x 12 / (2 x 6) = 50 LF |
| Linear Feet to Square Feet | LF x W" / 12 = SF | 40 LF of 1x6: 40 x 6 / 12 = 20 SF |
| Square Feet to Linear Feet | SF x 12 / W" = LF | 100 SF using 1x8: 100 x 12 / 8 = 150 LF |
| Square Feet to Board Feet | SF x T" = BF | 100 SF of 3/4" flooring: 100 x 0.75 = 75 BF |
| Board Feet to Square Feet | BF / T" = SF | 200 BF of 1" planks: 200 / 1 = 200 SF |
Pro Tip: When to Use Which Unit
Use Linear Feet when...
Buying standard-profile material like trim, molding, deck boards, or fence pickets where the cross-section is already defined.
Use Board Feet when...
Buying rough lumber, hardwoods, reclaimed wood, or any material priced by volume. This is the standard for our reclaimed stock.
Use Square Feet when...
Calculating coverage for flooring, wall paneling, decking, or any application where you need to know how much surface area will be covered.
Need Help Sizing Your Order?
Our team can help you calculate board feet, account for waste, and find the right reclaimed dimensions for your project.