Lumber Size Guide — Complete Reference
Nominal vs actual dimensions, board foot calculations, hardwood thickness fractions, beam sizes, weight estimates, and ordering tips for reclaimed lumber.
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Fundamental Concept
Nominal vs Actual Dimensions
One of the most confusing aspects of buying lumber is the difference between nominal and actual dimensions. A “2x4” doesn't actually measure 2 inches by 4 inches. The nominal size refers to the rough-sawn dimension before the board is dried and planed to its finished size.
Softwood (Dimensional Lumber)
For softwood lumber (Pine, Fir, Cedar, Spruce), the actual dimensions are standardized by the American Lumber Standard Committee (ALSC). After kiln drying and planing:
- • Boards under 2" nominal lose 1/4" per dimension when surfaced dry
- • Boards 2" to 6" nominal lose 1/2" per dimension
- • Boards 8" and over nominal lose 3/4" in width
- • Timbers (5"+) lose 1/2" per dimension
Hardwood Lumber
Hardwood is sold differently — by thickness in quarter-inch increments (4/4, 5/4, 6/4, etc.) and by the board foot. Width and length vary per board.
- • Rough thickness matches the nominal quarter fraction
- • Surfaced (S2S) thickness is approximately 3/16" less than rough
- • Width is random — you buy what the tree produced
- • Length is sold in 1-foot increments, typically 4' to 16'
Reclaimed lumber note: Reclaimed softwood often comes in true nominal dimensions (a reclaimed 2x4 may actually measure 2" x 4") because it was milled before modern surfacing standards were adopted. Always verify dimensions when ordering reclaimed — many customers are pleasantly surprised to find they're getting more wood than expected.
Complete Reference
Softwood Dimensional Lumber — Nominal vs Actual
Standard surfaced-dry (S-Dry / S4S) dimensions per ALSC PS 20. These apply to new lumber; reclaimed boards from pre-1960s structures may measure at or near full nominal.
| 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 |
| 3 x 3 | 2-1/2 x 2-1/2 | 64 x 64 |
| 3 x 4 | 2-1/2 x 3-1/2 | 64 x 89 |
| 3 x 6 | 2-1/2 x 5-1/2 | 64 x 140 |
| 3 x 8 | 2-1/2 x 7-1/4 | 64 x 184 |
| 3 x 10 | 2-1/2 x 9-1/4 | 64 x 235 |
| 3 x 12 | 2-1/2 x 11-1/4 | 64 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 |
| 4 x 8 | 3-1/2 x 7-1/4 | 89 x 184 |
| 4 x 10 | 3-1/2 x 9-1/4 | 89 x 235 |
| 4 x 12 | 3-1/2 x 11-1/4 | 89 x 286 |
| 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 |
| 6 x 10 | 5-1/2 x 9-1/2 | 140 x 241 |
| 6 x 12 | 5-1/2 x 11-1/2 | 140 x 292 |
| 8 x 8 | 7-1/2 x 7-1/2 | 190 x 190 |
| 8 x 10 | 7-1/2 x 9-1/2 | 190 x 241 |
| 8 x 12 | 7-1/2 x 11-1/2 | 190 x 292 |
| 10 x 10 | 9-1/2 x 9-1/2 | 241 x 241 |
| 10 x 12 | 9-1/2 x 11-1/2 | 241 x 292 |
| 12 x 12 | 11-1/2 x 11-1/2 | 292 x 292 |
Dimensions per American Lumber Standard Committee PS 20. Green (unseasoned) lumber may be 1/32" larger in thickness/width. Lengths are sold in 2-foot increments (8', 10', 12', etc.).
Hardwood Reference
Hardwood Thickness — Quarter System
Hardwood is sold by “quarters” — the number of quarter-inch increments in the rough board's thickness. A 4/4 board is four quarters (1 inch) thick before surfacing; 8/4 is two inches, and so on.
| Quarter | Nominal | Rough | Rough (mm) | Surfaced (S2S) | Surfaced (mm) | Common Uses |
|---|---|---|---|---|---|---|
| 4/4 | 1" | 1" | 25.4 mm | 13/16" | 20.6 mm | Shelving, paneling, light furniture components |
| 5/4 | 1-1/4" | 1-1/4" | 31.8 mm | 1-1/16" | 27.0 mm | Decking, stair treads, tabletops |
| 6/4 | 1-1/2" | 1-1/2" | 38.1 mm | 1-5/16" | 33.3 mm | Countertops, workbenches, heavy tabletops |
| 8/4 | 2" | 2" | 50.8 mm | 1-13/16" | 46.0 mm | Thick countertops, turning blanks, mantels |
| 10/4 | 2-1/2" | 2-1/2" | 63.5 mm | 2-5/16" | 58.7 mm | Heavy-duty countertops, timber frames, large turnings |
| 12/4 | 3" | 3" | 76.2 mm | 2-13/16" | 71.4 mm | Structural components, heavy furniture, stair newels |
| 16/4 | 4" | 4" | 101.6 mm | 3-13/16" | 96.8 mm | Posts, large turnings, sculptural blanks, timber work |
S2S vs S4S
S2S (Surfaced 2 Sides) means the board is planed on both faces but edges remain rough. S4S (Surfaced 4 Sides) means all four faces are planed smooth. S2S retains maximum width while giving you flat reference surfaces.
Reclaimed Hardwood
Reclaimed hardwood thickness varies by source. Old flooring stock is typically 3/4" finished. Reclaimed barn timbers often yield hardwood boards thicker than standard quarter fractions. Our custom milling service can surface any reclaimed hardwood to your exact specification.
Essential Calculation
Board Foot Calculation
The board foot (BF) is the standard unit of measure for hardwood lumber and many reclaimed products. One board foot equals a piece of wood 1 inch thick, 12 inches wide, and 12 inches long — or 144 cubic inches.
The Formula
BF = (T × W × L) ÷ 144
Where T = thickness in inches, W = width in inches, L = length in inches
Alternate formula (length in feet):
BF = (T × W × L) ÷ 12
Where T = thickness in inches, W = width in inches, L = length in feet
Example 1
A 1" thick x 6" wide x 8' long board
(1 x 6 x 8) / 12 = 4 BF
Example 2
A 2" thick x 10" wide x 12' long board
(2 x 10 x 12) / 12 = 20 BF
Example 3
An 8/4 (2") x 7" wide x 10' long hardwood
(2 x 7 x 10) / 12 = 11.67 BF
Quick Board Foot Reference — 1" Thick Boards
| Width | 6' long | 8' long | 10' long | 12' long | 16' long |
|---|---|---|---|---|---|
| 4" | 2.0 | 2.7 | 3.3 | 4.0 | 5.3 |
| 6" | 3.0 | 4.0 | 5.0 | 6.0 | 8.0 |
| 8" | 4.0 | 5.3 | 6.7 | 8.0 | 10.7 |
| 10" | 5.0 | 6.7 | 8.3 | 10.0 | 13.3 |
| 12" | 6.0 | 8.0 | 10.0 | 12.0 | 16.0 |
Key Distinction
Linear Foot vs Board Foot
These two units of measure cause more confusion than almost anything else in the lumber world. Understanding the difference is essential for accurate ordering and cost estimation.
Linear Foot (LF)
A linear foot measures length only — it's simply 12 inches of a board, regardless of width or thickness. It's commonly used for:
- • Trim, molding, and baseboards
- • Dimensional framing lumber (2x4, 2x6, etc.)
- • Decking boards
- • Fencing material
Board Foot (BF)
A board foot measures volume — thickness × width × length. It accounts for how much wood you're actually getting. It's the standard for:
- • Hardwood lumber (Oak, Maple, Walnut, etc.)
- • Reclaimed lumber of varying dimensions
- • Wholesale/mill-direct purchases
- • Wide planks and thick stock
Conversion example: A 2x6 that is 8 feet long is 8 linear feet. In board feet: (2 × 6 × 8) ÷ 12 = 8 board feet. A wider board of the same length would be more board feet but still the same linear feet.
Structural Reference
Common Beam & Timber Sizes
Weight estimates are for Douglas Fir at 12% moisture content. Actual weight varies by species and moisture level. Span ratings are approximate for residential applications — always consult an engineer for structural calculations.
| Nominal | Actual (in) | Wt/ft (lbs) | Typical Span | Common Use |
|---|---|---|---|---|
| 4 x 4 | 3-1/2 x 3-1/2 | 3.6 lb | Up to 4 ft | Posts, light framing, pergola members |
| 4 x 6 | 3-1/2 x 5-1/2 | 5.7 lb | Up to 6 ft | Porch beams, headers, decorative spans |
| 4 x 8 | 3-1/2 x 7-1/4 | 7.5 lb | Up to 8 ft | Floor beams, headers, ridge beams |
| 6 x 6 | 5-1/2 x 5-1/2 | 8.9 lb | Up to 8 ft | Posts, columns, mid-span beams |
| 6 x 8 | 5-1/2 x 7-1/2 | 12.2 lb | Up to 10 ft | Primary beams, exposed ceiling beams |
| 6 x 10 | 5-1/2 x 9-1/2 | 15.4 lb | Up to 12 ft | Main girders, long-span exposed beams |
| 6 x 12 | 5-1/2 x 11-1/2 | 18.7 lb | Up to 14 ft | Primary structural beams, barn restorations |
| 8 x 8 | 7-1/2 x 7-1/2 | 16.6 lb | Up to 12 ft | Heavy posts, major beams, timber frames |
| 8 x 10 | 7-1/2 x 9-1/2 | 21.0 lb | Up to 14 ft | Long-span beams, heavy commercial work |
| 8 x 12 | 7-1/2 x 11-1/2 | 25.5 lb | Up to 16 ft | Major structural beams, bridge timbers |
| 10 x 10 | 9-1/2 x 9-1/2 | 26.6 lb | Up to 16 ft | Heavy timber frames, commercial structures |
| 12 x 12 | 11-1/2 x 11-1/2 | 39.0 lb | Up to 20 ft | Major structural posts, bridge members |
Reclaimed beams often exceed modern dimensions. Historic timbers commonly measured at full nominal or even slightly oversize. Always verify individual beam measurements.
Planning & Logistics
Weight Estimation by Species
Knowing the approximate weight of your lumber order is essential for transportation planning, structural calculations, and freight cost estimates. All values at 12% moisture content (air-dried / kiln-dried).
| Species | lbs / Board Foot | lbs / cu ft | kg / m³ | Density Class |
|---|---|---|---|---|
| Douglas Fir | 2.8 | 34 | 545 | Medium-High |
| White Oak | 3.9 | 47 | 753 | High |
| Red Oak | 3.6 | 44 | 705 | High |
| Heart Pine | 3.4 | 41 | 657 | Medium-High |
| Redwood | 2.3 | 28 | 449 | Medium-Low |
| Western Red Cedar | 1.9 | 23 | 368 | Low |
| American Chestnut | 2.5 | 30 | 481 | Medium |
| Hard Maple | 3.7 | 44 | 705 | High |
| Black Walnut | 3.2 | 38 | 609 | Medium-High |
| Cherry | 2.9 | 35 | 561 | Medium |
| Yellow Pine | 3.2 | 39 | 625 | Medium-High |
| White Pine | 2.1 | 25 | 401 | Low |
Estimate Total Weight
Multiply total board feet by the lbs/BF value for your species. Example: 200 BF of White Oak ≈ 200 × 3.9 = 780 lbs.
Moisture Matters
Green (freshly cut) wood can weigh 50-100% more than kiln-dried. Reclaimed wood from covered structures is typically 12-18% MC. Our kiln-dried stock is 6-8%.
Delivery Planning
Our standard delivery trucks handle up to 5,000 lbs. For larger orders, we arrange flatbed transport throughout the Pacific Northwest.
Pro Tips
Tips for Ordering Reclaimed Lumber by Size
Reclaimed lumber has unique sizing considerations compared to buying new from a big-box store. These tips will help you get exactly what you need.
Measure Actual, Not Nominal
Always specify actual desired dimensions when ordering reclaimed. A reclaimed "2x6" might actually be 2" x 6", 1-3/4" x 5-3/4", or 1-1/2" x 5-1/2" depending on its era and source. We'll match you with inventory that meets your actual needs.
Order 10-15% Extra
Reclaimed lumber inevitably has some sections with hidden defects, end checks, or character that may not suit your specific application. Ordering 10-15% overage ensures you have enough clean material to complete your project.
Specify Your Application
Tell us what the wood will be used for — flooring, framing, furniture, accent wall. This helps us pull appropriate material. Structural applications have different requirements than decorative ones.
Consider Custom Milling
If you need a specific thickness, width, or profile that doesn't match our stock sizes, our custom milling service can rip, resaw, plane, or profile reclaimed stock to any dimension. See our milling page for details.
Ask About Mixed Widths
For flooring and paneling, mixed-width installations create beautiful visual interest and allow us to use more of each salvaged board. Specify a width range (e.g., 4"-8") rather than a single dimension to maximize yield and lower cost.
Length Availability Varies
Reclaimed boards are limited by their original structure. 8' and 10' lengths are most common. Lengths over 12' may require longer lead times. For beams, we regularly carry timbers up to 20' and can source longer pieces on request.
Request Samples First
For large orders, we recommend requesting samples or visiting our Portland yard. Seeing the actual species, grade, and patina in person ensures the material matches your vision before you commit to a full order.
Understand Board Foot Pricing
Reclaimed lumber is typically priced per board foot, not per linear foot. Use the calculator above to estimate your total board footage, then contact us for a quote. Volume discounts are available for orders over 500 BF.
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