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Why Nominal and Actual Sizes Are Different
When you buy a “2x4,” the board you receive is actually 1-1/2″ by 3-1/2″. This is not a trick — it's the result of how lumber is manufactured. The “nominal” size (2x4) refers to the rough-sawn dimensions of the board right after it comes off the saw. After the board is dried (either air-dried or kiln-dried) and planed smooth on all four sides (S4S), it shrinks and loses material, resulting in the smaller “actual” dimensions.
This standard has been in place since 1964 when the American Lumber Standard Committee established uniform sizing. Before that, a 2x4 could vary from mill to mill. Today, all commercially sold dimensional lumber in the United States follows the same sizing conventions set by the National Institute of Standards and Technology (NIST) under PS 20.
Important note about reclaimed lumber: Vintage and reclaimed lumber often has dimensions closer to their nominal size because older milling practices removed less material. A reclaimed 2x4 from the early 1900s may measure a full 2″ by 4″ or very close to it. This is one reason reclaimed lumber is prized for restoration work where matching historic dimensions is essential.
Softwood Dimensional Lumber — Nominal vs Actual
These are the standard dimensions for surfaced (S4S) softwood lumber such as pine, fir, spruce, and cedar. Boards under 2″ nominal thickness lose 1/4″ when dried and surfaced; boards 2″ and thicker lose 1/2″.
Board Lumber (Under 2″ Nominal Thickness)
| Nominal Size | Actual Size (inches) | Actual Size (mm) | Common Uses |
|---|---|---|---|
| 1 x 2 | 3/4″ x 1-1/2″ | 19 x 38 | Furring strips, shims, craft projects |
| 1 x 3 | 3/4″ x 2-1/2″ | 19 x 64 | Trim, strapping, lattice |
| 1 x 4 | 3/4″ x 3-1/2″ | 19 x 89 | Trim, shelving, craft projects |
| 1 x 6 | 3/4″ x 5-1/2″ | 19 x 140 | Fence boards, shelving, paneling |
| 1 x 8 | 3/4″ x 7-1/4″ | 19 x 184 | Shelving, sheathing, siding |
| 1 x 10 | 3/4″ x 9-1/4″ | 19 x 235 | Shelving, cabinet sides, wide trim |
| 1 x 12 | 3/4″ x 11-1/4″ | 19 x 286 | Wide shelving, cabinet work, siding |
Dimensional Lumber (2″ and Thicker)
| 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 | Light framing, furring, studs |
| 2 x 4 | 1-1/2″ x 3-1/2″ | 38 x 89 | Wall framing, general construction |
| 2 x 6 | 1-1/2″ x 5-1/2″ | 38 x 140 | Wall framing, floor joists, 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, rafters, headers, beams |
| 2 x 12 | 1-1/2″ x 11-1/4″ | 38 x 286 | Floor joists, ridge boards, stair stringers |
| 4 x 4 | 3-1/2″ x 3-1/2″ | 89 x 89 | Posts, columns, railings |
| 4 x 6 | 3-1/2″ x 5-1/2″ | 89 x 140 | Posts, beams, heavy framing |
| 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 | Beams, heavy construction, timber frames |
| 8 x 8 | 7-1/2″ x 7-1/2″ | 190 x 190 | Large posts, timber framing, bridges |
| 10 x 10 | 9-1/2″ x 9-1/2″ | 241 x 241 | Heavy timber framing, large structural posts |
| 12 x 12 | 11-1/2″ x 11-1/2″ | 292 x 292 | Structural columns, large beams, piers |
Plywood & Panel Dimensions
Plywood and sheet goods are sold in standard panel sizes, most commonly 4 feet by 8 feet (48″ x 96″). Unlike dimensional lumber, plywood thickness is usually stated as the actual thickness, though minor variations (up to 1/32″) can occur due to sanding and manufacturing tolerances. Understanding panel sizes is essential for sheathing, subfloor, cabinetry, and built-in projects.
Note: Plywood is also available in 5' x 5' sheets (common for Baltic Birch) and 4' x 10' sheets for specialty applications. Metric-sized panels (1220 mm x 2440 mm) are the international standard equivalent.
Standard Plywood Thicknesses
| Nominal Thickness | Actual Thickness | Metric Equivalent | Common Uses | Weight per 4x8 Sheet (approx.) |
|---|---|---|---|---|
| 1/8″ | 7/64″ | 3 mm | Drawer bottoms, cabinet backs, craft projects, templates | 6–8 lbs |
| 1/4″ | 7/32″ | 6 mm | Cabinet backs, underlayment, paneling, curved forms | 12–15 lbs |
| 3/8″ | 11/32″ | 9 mm | Sheathing, light shelving, shop jigs, subflooring underlayment | 18–22 lbs |
| 1/2″ | 15/32″ | 12 mm | Wall sheathing, cabinet sides, shelving, subfloor | 25–32 lbs |
| 5/8″ | 19/32″ | 15 mm | Roof sheathing, subflooring, heavy shelving | 35–42 lbs |
| 3/4″ | 23/32″ | 18 mm | Subflooring, countertops, cabinet carcasses, furniture, workbenches | 44–55 lbs |
| 1″ | 31/32″ | 25 mm | Heavy-duty shelving, countertops, stair treads, workbench tops | 58–70 lbs |
| 1-1/8″ | 1-1/8″ | 28 mm | Industrial subflooring, heavy structural applications, trailer decking | 70–85 lbs |
Common Panel Sheet Sizes
| Sheet Size | Dimensions (in) | Dimensions (mm) | Area (sq ft) | Notes |
|---|---|---|---|---|
| 4' x 8' | 48 x 96 | 1,220 x 2,440 | 32 sq ft | Standard U.S. sheet; most common size for all panel products |
| 4' x 10' | 48 x 120 | 1,220 x 3,050 | 40 sq ft | Taller walls without seams; special order at most yards |
| 5' x 5' | 60 x 60 | 1,525 x 1,525 | 25 sq ft | Baltic Birch standard; ideal for CNC and cabinet work |
| 4' x 4' | 48 x 48 | 1,220 x 1,220 | 16 sq ft | Half sheets; easier to transport and handle for small projects |
| 2' x 4' | 24 x 48 | 610 x 1,220 | 8 sq ft | Project panels (pre-cut); available at home centers for small jobs |
How to Calculate Board Feet
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). Board feet are used to price hardwoods, reclaimed lumber, and specialty woods.
The Board Foot Formula
Board Feet = (Thickness × Width × Length) ÷ 144
All dimensions in inches. Use nominal thickness and width; actual length.
Alternative formula for length in feet: Board Feet = (Thickness in inches × Width in inches × Length in feet) ÷ 12
Quick shortcut for 1″ thick lumber: Multiply the width in inches by the length in feet, then divide by 12. For example, a 1x8 that is 10 feet long: (8 × 10) ÷ 12 = 6.67 BF.
For multiple boards: Calculate the board feet per piece, then multiply by the number of pieces. Always round up to the nearest whole board foot when ordering.
Board Foot Calculation Examples
| Board Size (Nominal) | Length | Calculation | Board Feet |
|---|---|---|---|
| 1 x 4 | 8 ft | (1 × 4 × 8) ÷ 12 | 2.67 BF |
| 1 x 6 | 8 ft | (1 × 6 × 8) ÷ 12 | 4 BF |
| 1 x 8 | 10 ft | (1 × 8 × 10) ÷ 12 | 6.67 BF |
| 1 x 12 | 12 ft | (1 × 12 × 12) ÷ 12 | 12 BF |
| 2 x 4 | 8 ft | (2 × 4 × 8) ÷ 12 | 5.33 BF |
| 2 x 6 | 10 ft | (2 × 6 × 10) ÷ 12 | 10 BF |
| 2 x 6 | 12 ft | (2 × 6 × 12) ÷ 12 | 12 BF |
| 2 x 8 | 14 ft | (2 × 8 × 14) ÷ 12 | 18.67 BF |
| 2 x 10 | 16 ft | (2 × 10 × 16) ÷ 12 | 26.67 BF |
| 2 x 12 | 16 ft | (2 × 12 × 16) ÷ 12 | 32 BF |
| 4 x 4 | 10 ft | (4 × 4 × 10) ÷ 12 | 13.33 BF |
| 4 x 6 | 12 ft | (4 × 6 × 12) ÷ 12 | 24 BF |
| 6 x 6 | 12 ft | (6 × 6 × 12) ÷ 12 | 36 BF |
| 6 x 8 | 16 ft | (6 × 8 × 16) ÷ 12 | 64 BF |
| 8 x 8 | 20 ft | (8 × 8 × 20) ÷ 12 | 106.67 BF |
| 10 x 10 | 24 ft | (10 × 10 × 24) ÷ 12 | 200 BF |
How Much Lumber Do I Need? — Project Estimates
Planning a project and not sure how much lumber to order? These estimates cover the most common DIY and contractor projects. All estimates include a 10–15% waste factor for cutting, defects, and errors. Actual quantities will vary based on your specific design, spacing, and local code requirements.
Pro tip: Send us your project plans or dimensions and our team will calculate exact quantities for you — free of charge.
| Project | Typical Size | Primary Lumber Needed | Estimated Board Feet | Notes |
|---|---|---|---|---|
| Ground-Level Deck | 12' x 16' (192 sq ft) | 2x6 decking, 2x8 joists, 4x4 posts | ~450–550 BF | Includes framing, decking, and fascia; excludes railing |
| Raised Deck with Railing | 16' x 20' (320 sq ft) | 2x6 decking, 2x10 joists, 6x6 posts, 2x4 railing | ~800–1,000 BF | Includes stairs, railing, and post hardware ledger |
| Privacy Fence | 100 linear ft, 6' tall | 1x6 pickets, 2x4 rails, 4x4 posts | ~350–425 BF | Dog-ear pickets at 8' on center post spacing; 3 rails per section |
| Accent Wall (Shiplap) | 10' x 8' (80 sq ft) | 1x6 shiplap boards, 1x2 furring strips | ~90–110 BF | Includes 15% waste factor for cuts and end matching |
| Garden Shed | 8' x 10' | 2x4 framing, 2x6 rafters, 1x6 siding, 3/4″ plywood floor | ~500–650 BF | Plus 5–7 sheets plywood; excludes roofing material and door |
| Pergola | 10' x 12' | 6x6 posts, 2x8 beams, 2x6 rafters, 2x2 lattice | ~250–350 BF | 4 post design; more for additional rafters and lattice density |
| Hardwood Flooring | 500 sq ft room | 3/4″ x 3-1/4″ T&G flooring | ~575–625 BF | 15% waste factor; tongue coverage reduces effective width |
| Barn Door | 3' x 7' (single) | 1x6 face boards, 1x4 Z-brace, 2x4 frame | ~25–35 BF | Reclaimed lumber adds character; hardware sold separately |
| Fireplace Mantel | 6' x 8″ x 6″ | 6x8 or 8x8 reclaimed beam | ~20–32 BF | Reclaimed heart pine or cypress; single-piece beams available |
| Bookshelf (Built-In) | 4' wide x 7' tall | 1x10 or 1x12 shelves, 1x2 face frame | ~45–65 BF | 6 shelves plus sides, top, and bottom; adjustable shelf pins |
| Dining Table | 3.5' x 7' | 8/4 hardwood for top, 4x4 legs, 2x4 apron | ~50–70 BF | Edge-glued tabletop from wide boards; species affects price significantly |
| Raised Garden Beds | 4' x 8' x 12″ (set of 3) | 2x12 or 2x6 stacked sides, 4x4 corner posts | ~120–160 BF | Use cedar, cypress, or reclaimed lumber for ground contact |
Standard Lumber Lengths
Lumber is sold in standard lengths, typically in 2-foot increments. The most common lengths available at lumberyards and home centers are listed below. Reclaimed lumber lengths may vary depending on the source material.
| Length (ft) | Length (m) | Availability | Notes |
|---|---|---|---|
| 8' | 2.44 m | Very Common | Standard stud length for 8' ceilings |
| 10' | 3.05 m | Very Common | Popular for floor joists and rafters |
| 12' | 3.66 m | Very Common | Versatile length for many framing applications |
| 14' | 4.27 m | Common | Used in wider spans, may cost more per foot |
| 16' | 4.88 m | Common | Maximum stocked length at many retail yards |
| 20' | 6.10 m | Special Order | Typically requires special order; limited sizes |
| 24' | 7.32 m | Rare | Available in select structural grades; premium pricing |
Common Lumber Packages & Bundles
When ordering lumber in larger quantities — especially for contractors and commercial projects — you will encounter standard bundle and unit sizes. Understanding these package quantities helps you order efficiently and compare prices between suppliers.
Bundle sizes vary by mill and product type. The quantities below are representative industry standards. Always confirm exact bundle counts with your supplier before ordering.
| Product | Typical Bundle Size | Pieces per Bundle | Board Feet per Bundle (approx.) | Notes |
|---|---|---|---|---|
| 2x4 Studs (8') | Pre-cut 92-5/8″ | 208 pcs | ~1,109 BF | Standard unit pack; banded and ready for jobsite |
| 2x4 (various lengths) | Unit | 294–364 pcs | ~2,000+ BF | Full unit; varies by mill and length |
| 2x6 (various lengths) | Unit | 128–189 pcs | ~2,000+ BF | Standard framing pack |
| 2x10 (various lengths) | Unit | 80–100 pcs | ~2,000+ BF | Joist and rafter packs |
| 1x6 Fence Boards (6') | Bundle | 250–400 pcs | ~750–1,200 BF | Dog-ear or flat top; varies by mill |
| Hardwood (random width) | 100 BF lots | Varies | 100 BF | Sold by board foot; random widths and lengths within the lot |
| Plywood (3/4″) | Lift / Unit | 48–60 sheets | — | 1,536–1,920 sq ft per lift; unit pricing saves 10–20% |
Softwood vs Hardwood Sizing
Softwood and hardwood lumber follow different sizing conventions. Understanding these differences is critical when planning a project that uses both types of wood.
Softwood Sizing
- Species: Pine, Fir, Spruce, Cedar
- Sold as: Nominal dimensions (2x4, 2x6, etc.)
- Thickness loss: 1/2″ for 2″+ nominal; 1/4″ for 1″ nominal
- Width loss: 1/2″ for 6″+ nominal; 1/4″ for under 6″ nominal
- Surfacing: S4S (surfaced four sides) is standard
- Pricing: Usually per linear foot or per piece
- Moisture content: 19% MC maximum for KD (kiln dried), S-DRY (surfaced dry)
Hardwood Sizing
- Species: Oak, Maple, Cherry, Walnut, Poplar
- Sold as: Quarter-inch increments (4/4, 5/4, 6/4, 8/4, etc.)
- 4/4 (four quarter): 1″ rough = 13/16″ surfaced
- 5/4 (five quarter): 1-1/4″ rough = 1-1/16″ surfaced
- 6/4 (six quarter): 1-1/2″ rough = 1-5/16″ surfaced
- 8/4 (eight quarter): 2″ rough = 1-13/16″ surfaced
- Width: Random widths; sold by the board foot
- Pricing: Per board foot (BF)
Hardwood Thickness Reference (Quarter System)
Hardwoods are measured in quarters of an inch. “4/4” means four quarters (one inch), “8/4” means eight quarters (two inches), and so on. The actual thickness after surfacing is less than the rough dimension.
| Quarter Designation | Rough Thickness | Surfaced (S2S) | Metric (Surfaced) |
|---|---|---|---|
| 3/4 | 3/4″ | 9/16″ | 14 mm |
| 4/4 | 1″ | 13/16″ | 21 mm |
| 5/4 | 1-1/4″ | 1-1/16″ | 27 mm |
| 6/4 | 1-1/2″ | 1-5/16″ | 33 mm |
| 8/4 | 2″ | 1-13/16″ | 46 mm |
| 10/4 | 2-1/2″ | 2-5/16″ | 59 mm |
| 12/4 | 3″ | 2-13/16″ | 71 mm |
| 16/4 | 4″ | 3-13/16″ | 97 mm |
Metric Conversion Reference
Quick conversions for working with international specifications or imported materials.
| Imperial | Metric | Imperial | Metric |
|---|---|---|---|
| 1/4″ | 6.35 mm | 1 foot | 304.8 mm / 0.305 m |
| 1/2″ | 12.7 mm | 8 feet | 2,438 mm / 2.44 m |
| 3/4″ | 19.05 mm | 10 feet | 3,048 mm / 3.05 m |
| 1″ | 25.4 mm | 12 feet | 3,658 mm / 3.66 m |
| 1-1/2″ | 38.1 mm | 16 feet | 4,877 mm / 4.88 m |
| 3-1/2″ | 88.9 mm | 20 feet | 6,096 mm / 6.10 m |
| 5-1/2″ | 139.7 mm | 1 board foot | 2,360 cm³ / 0.00236 m³ |
Metric Conversion Formulas
Length Conversions
- Inches to mm: multiply by 25.4
- mm to inches: divide by 25.4
- Feet to meters: multiply by 0.3048
- Meters to feet: multiply by 3.281
- Inches to cm: multiply by 2.54
- cm to inches: divide by 2.54
Area & Volume Conversions
- Square feet to m²: multiply by 0.0929
- m² to square feet: multiply by 10.764
- Board feet to m³: multiply by 0.00236
- m³ to board feet: multiply by 423.78
- Cubic feet to m³: multiply by 0.02832
- 1 board foot = 1/12 cubic foot = 2,360 cm³
Weight Conversions
- Pounds to kg: multiply by 0.4536
- kg to pounds: multiply by 2.205
- lb/ft³ to kg/m³: multiply by 16.02
- kg/m³ to lb/ft³: divide by 16.02
Pressure / Strength Conversions
- psi to MPa: divide by 145.04
- MPa to psi: multiply by 145.04
- lbf (Janka) to N: multiply by 4.448
- N to lbf: divide by 4.448
Tips for Ordering the Right Dimensions
1. Always Specify Whether You Mean Nominal or Actual
When placing an order, clarify whether you need nominal or actual dimensions. Saying “I need a 2x4” is understood as nominal (actual 1.5″ x 3.5″). If you need a board that is truly 2″ by 4″, specify “full dimension” or “rough sawn.”
2. Account for Waste and Cutting
Order 10-15% more lumber than your calculated needs. Cutting waste, defective pieces, and measuring errors are inevitable. For complex projects with many angled cuts, consider ordering 20% extra.
3. Check Moisture Content
Green (wet) lumber will shrink as it dries. If you're buying green lumber, the actual dimensions will be slightly larger than surfaced dry lumber but will shrink further. Kiln-dried (KD) lumber is dimensionally stable at the sizes listed in the tables above.
4. Reclaimed Lumber Dimensions Vary
Reclaimed lumber often comes in non-standard sizes. A reclaimed “2x4” may be true 2″ x 4″ or anywhere in between. Always verify dimensions before ordering, and consider having reclaimed lumber resawn or planed to a consistent size if uniformity is important for your project.
5. Use Board Feet for Cost Comparison
When comparing prices between suppliers, convert everything to price-per-board-foot for an apples-to-apples comparison. This is especially useful when comparing reclaimed lumber (sold by BF) with dimensional lumber (sold by the piece or linear foot).
6. Know Your Plywood Span Ratings
Plywood used for structural sheathing carries a span rating (e.g., 32/16) that indicates the maximum support spacing for roof/floor applications. A 32/16 panel can span 32″ on-center for roofs and 16″ on-center for floors. Always check the APA span rating stamp before using plywood structurally.
7. Plan for Tongue-and-Groove Coverage Loss
When ordering tongue-and-groove (T&G) flooring or paneling, remember that the tongue reduces the effective coverage width. A 1x6 T&G board typically covers only about 5-1/8″ of width, not the full 5-1/2″ face. Order approximately 15–20% more T&G material than bare square footage suggests.
Sizing FAQ
Answers to the most common questions about lumber dimensions, sizing, and ordering quantities.