Lumber Sizing Guide
Everything you need to know about lumber dimensions, board foot calculations, coverage planning, and how to order the right amount for your project.
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Key takeaway: Lumber is sold by its nominalsize (e.g., 2x4), but the actual dimensions are smaller due to drying and planing. A nominal 2x4 actually measures 1.5" x 3.5". Reclaimed lumber may be closer to true nominal dimensions if it was cut before modern sizing standards took effect in the 1960s.
Nominal vs. Actual Dimensions
The lumber industry uses a system where the "name" of a board (its nominal size) differs from its actual measured dimensions. This dates back to when lumber was sold in rough-sawn dimensions and then planed smooth, removing about 1/2 inch from each face. Modern lumber follows the American Softwood Lumber Standard (PS 20) established by NIST.
When boards are kiln-dried after rough sawing, further shrinkage occurs. The combination of drying shrinkage and surfacing planing accounts for the full difference between nominal and actual. For posts and timbers (sizes 5x5 and larger), the planing allowance is smaller, so the actual dimension is closer to the nominal — but still not equal.
| Nominal | Actual (inches) | Actual (mm) | Board Ft per LF | Weight/ft (Doug Fir) |
|---|---|---|---|---|
| 1x2 | 0.75 x 1.5 | 19 x 38 | 0.17 | 0.3 lb |
| 1x3 | 0.75 x 2.5 | 19 x 64 | 0.25 | 0.5 lb |
| 1x4 | 0.75 x 3.5 | 19 x 89 | 0.33 | 0.7 lb |
| 1x6 | 0.75 x 5.5 | 19 x 140 | 0.50 | 1.0 lb |
| 1x8 | 0.75 x 7.25 | 19 x 184 | 0.67 | 1.4 lb |
| 1x10 | 0.75 x 9.25 | 19 x 235 | 0.83 | 1.7 lb |
| 1x12 | 0.75 x 11.25 | 19 x 286 | 1.00 | 2.1 lb |
| 2x2 | 1.5 x 1.5 | 38 x 38 | 0.33 | 0.5 lb |
| 2x4 | 1.5 x 3.5 | 38 x 89 | 0.67 | 1.3 lb |
| 2x6 | 1.5 x 5.5 | 38 x 140 | 1.00 | 2.0 lb |
| 2x8 | 1.5 x 7.25 | 38 x 184 | 1.33 | 2.6 lb |
| 2x10 | 1.5 x 9.25 | 38 x 235 | 1.67 | 3.4 lb |
| 2x12 | 1.5 x 11.25 | 38 x 286 | 2.00 | 4.1 lb |
| 4x4 | 3.5 x 3.5 | 89 x 89 | 1.33 | 3.6 lb |
| 4x6 | 3.5 x 5.5 | 89 x 140 | 2.00 | 5.6 lb |
| 4x8 | 3.5 x 7.25 | 89 x 184 | 2.67 | 7.4 lb |
| 6x6 | 5.5 x 5.5 | 140 x 140 | 3.00 | 8.8 lb |
| 6x8 | 5.5 x 7.5 | 140 x 191 | 4.17 | 12.0 lb |
| 6x10 | 5.5 x 9.5 | 140 x 241 | 5.00 | 15.2 lb |
| 8x8 | 7.5 x 7.5 | 191 x 191 | 5.33 | 16.3 lb |
| 8x10 | 7.5 x 9.5 | 191 x 241 | 6.67 | 20.7 lb |
| 10x10 | 9.5 x 9.5 | 241 x 241 | 8.33 | 26.1 lb |
| 12x12 | 11.5 x 11.5 | 292 x 292 | 12.00 | 38.3 lb |
Reclaimed Lumber Sizing Differences
Reclaimed lumber often has different actual dimensions than modern stock. Pre-1960s lumber was typically milled to full nominal dimensions (a vintage 2x4 may actually measure 2" x 4"). After processing through our mill, reclaimed lumber is sized to either:
- ✓ Modern standard dimensions — to match new lumber on the same project
- ✓ Custom dimensions — to match existing reclaimed installations
- ✓ Full nominal — when the larger size is a feature, not a bug
When mixing reclaimed and new lumber on the same project, verify actual dimensions before installing. A reclaimed 2x6 from a 1940s factory may measure 1.75" x 5.75" rather than the modern 1.5" x 5.5", creating a 1/4" discrepancy that affects flooring alignment, wall framing, and trim fitting. Always measure before you cut.
| Nominal | Modern Actual | Pre-1965 Actual | Typical Reclaimed (as-salvaged) |
|---|---|---|---|
| 2x4 | 1.5" x 3.5" | 1.625" x 3.625" | 1.75" x 3.75" to 2" x 4" |
| 2x6 | 1.5" x 5.5" | 1.625" x 5.625" | 1.75" x 5.75" to 2" x 6" |
| 2x8 | 1.5" x 7.25" | 1.625" x 7.5" | 1.75" x 7.5" to 2" x 8" |
| 2x10 | 1.5" x 9.25" | 1.625" x 9.5" | 1.75" x 9.75" to 2" x 10" |
| 2x12 | 1.5" x 11.25" | 1.625" x 11.5" | 1.75" x 11.75" to 2" x 12" |
| 6x6 | 5.5" x 5.5" | 5.625" x 5.625" | 5.75" x 5.75" to 6" x 6" |
| 8x8 | 7.5" x 7.5" | 7.625" x 7.625" | 7.75" x 7.75" to 8" x 8" |
How to Calculate Board Feet
Lumber is sold by the board foot (BF). One board foot equals a piece of wood 1 inch thick, 12 inches wide, and 12 inches long (144 cubic inches). Board footage is calculated using nominal dimensions, not actual — this is standard industry practice.
Board Feet = (Thickness" × Width" × Length") ÷ 144
Where all dimensions are in inches. For length in feet, simplify to:
Board Feet = (Thickness" × Width" × Length') ÷ 12
Use nominal dimensions (e.g., 2, 4, 6) rather than actual (1.5, 3.5, 5.5) in this formula — the industry standard is nominal-based pricing.
Example Calculations
One 2x6, 8 feet long: (2 × 6 × 8) ÷ 12 = 8 board feet
Ten 2x4s, 12 feet long: 10 × (2 × 4 × 12) ÷ 12 = 80 board feet
One 6x8 beam, 16 feet: (6 × 8 × 16) ÷ 12 = 64 board feet
100 linear feet of 1x6 flooring: (1 × 6 × 100) ÷ 12 = 50 board feet
One 10x10 post, 12 feet: (10 × 10 × 12) ÷ 12 = 100 board feet
Coverage: Square Feet per Board Foot
When planning flooring, paneling, or decking projects, you need to convert between square feet of coverage and board feet of material. The table below shows how much surface area one board foot covers for common sizes, accounting for standard installation gaps and waste factors. Always add a 10–15% overage for end cuts, defects, and layout waste; add 15–20% for diagonal installations.
| Board Size | Face Width (actual) | Sq Ft / Board Ft (no gap) | Sq Ft / Board Ft (1/8" gap) | Board Ft per 100 sq ft | Common Use |
|---|---|---|---|---|---|
| 1x4 | 3.5" | 1.4 sq ft | 1.35 sq ft | 74 BF | Ceiling, accent wall |
| 1x6 | 5.5" | 1.1 sq ft | 1.07 sq ft | 94 BF | Shiplap, paneling, flooring |
| 1x8 | 7.25" | 0.97 sq ft | 0.94 sq ft | 107 BF | Wide-plank flooring, siding |
| 1x10 | 9.25" | 0.91 sq ft | 0.88 sq ft | 114 BF | Wide-plank paneling |
| 1x12 | 11.25" | 0.94 sq ft | 0.91 sq ft | 110 BF | Wide-plank flooring, barn door |
| 2x6 | 5.5" | 0.55 sq ft | 0.54 sq ft | 188 BF | Decking (face-up) |
| 2x8 | 7.25" | 0.60 sq ft | 0.59 sq ft | 170 BF | Decking, boardwalk |
| 2x10 | 9.25" | 0.62 sq ft | 0.60 sq ft | 167 BF | Heavy decking |
| 5/4x6 | 5.5" | 1.10 sq ft | 1.07 sq ft | 94 BF | Standard decking |
Waste factor guidance:Standard straight installation: add 10%. Diagonal (>30°): add 15%. Herringbone or parquet pattern: add 20%. Irregular-shaped rooms: add 15%. Very rustic reclaimed stock with high defect rate: add 20–25%.
Weight by Species
Wood density varies significantly by species and moisture content. The following table shows approximate weight per board foot at typical air-dried moisture content (12–15%). Green (freshly sawn) wood can weigh 50–100% more. This data is critical for structural load calculations, transportation planning, and floor load assessments.
| Species | Density (lb/ft³) | Weight per BF (dry) | Weight per BF (green) | 100 BF Dry Weight |
|---|---|---|---|---|
| Black Locust | 48 lb/ft³ | 4.0 lb | 6.8 lb | 400 lb |
| White Oak | 47 lb/ft³ | 3.9 lb | 6.4 lb | 390 lb |
| Hard Maple | 44 lb/ft³ | 3.7 lb | 5.8 lb | 370 lb |
| Red Oak | 44 lb/ft³ | 3.7 lb | 5.8 lb | 370 lb |
| Hickory | 51 lb/ft³ | 4.3 lb | 7.2 lb | 430 lb |
| Ash | 42 lb/ft³ | 3.5 lb | 5.6 lb | 350 lb |
| Black Walnut | 38 lb/ft³ | 3.2 lb | 5.0 lb | 320 lb |
| Heart Pine (SYP) | 36 lb/ft³ | 3.0 lb | 5.6 lb | 300 lb |
| Douglas Fir | 32 lb/ft³ | 2.7 lb | 4.8 lb | 270 lb |
| Cypress | 32 lb/ft³ | 2.7 lb | 4.8 lb | 270 lb |
| Hemlock | 29 lb/ft³ | 2.4 lb | 4.2 lb | 240 lb |
| Poplar | 28 lb/ft³ | 2.3 lb | 3.8 lb | 230 lb |
| Western Red Cedar | 23 lb/ft³ | 1.9 lb | 3.4 lb | 190 lb |
| Sitka Spruce | 28 lb/ft³ | 2.3 lb | 3.8 lb | 230 lb |
International & Metric Size Conversions
If you are working with imported materials, European drawings, or shipping to international destinations, you will encounter metric lumber sizing. European and Australian lumber uses different nominal conventions than North American sizes. The table below maps the most common nominal conversions and notes where standard sizes differ significantly.
| US Nominal | US Actual (in) | US Actual (mm) | European Equivalent (mm) | Australian Equivalent (mm) | Notes |
|---|---|---|---|---|---|
| 1x4 | 0.75 x 3.5" | 19 x 89 | 22 x 90 | 19 x 90 | Closest metric: 22x90 |
| 1x6 | 0.75 x 5.5" | 19 x 140 | 22 x 140 | 19 x 140 | Width matches exactly |
| 2x4 | 1.5 x 3.5" | 38 x 89 | 47 x 100 | 45 x 90 | EU is wider and thicker |
| 2x6 | 1.5 x 5.5" | 38 x 140 | 47 x 147 | 45 x 140 | Close match in width |
| 2x8 | 1.5 x 7.25" | 38 x 184 | 47 x 194 | 45 x 185 | Near equivalent |
| 2x10 | 1.5 x 9.25" | 38 x 235 | 47 x 244 | 45 x 240 | Near equivalent |
| 4x4 | 3.5 x 3.5" | 89 x 89 | 100 x 100 | 90 x 90 | Metric is slightly larger |
| 6x6 | 5.5 x 5.5" | 140 x 140 | 150 x 150 | 140 x 140 | AU matches, EU slightly larger |
| 8x8 | 7.5 x 7.5" | 190 x 190 | 200 x 200 | 190 x 190 | AU matches, EU slightly larger |
Quick Unit Conversions
Length: 1 inch = 25.4 mm | 1 foot = 304.8 mm | 1 meter = 39.37 inches
Area: 1 sq ft = 0.0929 m² | 1 m² = 10.764 sq ft
Volume: 1 board foot = 2,360 cm³ | 1 m³ = 424 board feet
Weight: 1 lb = 0.4536 kg | 1 kg = 2.205 lb
Density: 1 lb/ft³ = 16.02 kg/m³
Board ft to lineal ft: LF = BF ÷ (nominal T" × W" ÷ 12)
Common Lengths & Standard Stock
New softwood lumber comes in standard 2-foot increments from 8' to 20'. Hardwood lumber is typically available in random lengths from 4' to 16'. Reclaimed lumber lengths depend on the source structure and often do not conform to standard increments — an advantage when you need odd lengths, and a planning challenge when you need precision cuts.
| Category | Typical Available Lengths | Reclaimed Availability | Notes |
|---|---|---|---|
| Softwood dimensional | 8', 10', 12', 14', 16' | Varies — depends on source building | Can cut to length from longer stock |
| Softwood studs | 8', 9', 10' | 7'–10' common | Ceiling height of source building determines stud length |
| Hardwood flooring | 6'–10' random length | Mixed: 2'–12' | Short pieces common; sort before ordering |
| Beams & timbers | 10'–24' | 12'–40' possible | Long reclaimed beams are a key advantage over new |
| Boards (1x) | 8'–16' | 4'–20' | Wider boards often shorter due to old-growth tree profile |
| Decking | 8'–20' | 10'–16' typical | Longer runs available from pier and dock salvage |
Need Help Calculating Your Order?
Not sure how much lumber you need? Send us your project dimensions and we will calculate the board footage, recommend sizes, account for waste factors, and provide a quote. We have helped hundreds of builders, designers, and contractors plan their material orders accurately. Contact us or try our Eco Impact Calculator.