Lumber Sizes Chart — Nominal vs Actual (Inches & MM)
Interactive dimensional lumber size chart. Inspect 1:1 true-scale physical cross-sections, convert nominal to actual dimensions in inches and millimeters, calculate board feet, and estimate lumber weight.
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📦 Board Foot & Weight Estimator
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Maximum allowable span under standard residential load (40 psf Live, 10 psf Dead, L/360):
Common Lumber Sizes: Nominal vs. Actual Quick Reference
In carpentry, architecture, and construction, lumber is referred to by its nominal dimensions (such as 2x4, 2x6, 2x8, 2x10, 4x4, or 6x6). However, the actual finished size of the lumber is smaller due to kiln drying shrinkage and 4-sided surface planing (S4S). Use this reference chart and 1:1 scale cross-section tool to look up exact dimensional measurements in fractional inches, decimal inches, and metric millimeters (mm).
Master Nominal vs. Actual Lumber Size Chart
Filter through all standard dimensional lumber sizes, boards, posts, and heavy timbers. View exact dimensions in decimal inches, fractions, and metric millimeters (mm).
| Nominal Size | Actual Size (Inches) | Actual Size (MM) | Category | Area (Sq.In) | Max Floor Joist Span (16″ OC) |
|---|---|---|---|---|---|
| 1" × 2" | 0.75″ × 1.5″ | 19 × 38 mm | 1x Boards | 1.13 in² | N/A (Furring) |
| 1" × 3" | 0.75″ × 2.5″ | 19 × 64 mm | 1x Boards | 1.88 in² | N/A |
| 1" × 4" | 0.75″ × 3.5″ | 19 × 89 mm | 1x Boards | 2.63 in² | N/A (Trim) |
| 1" × 6" | 0.75″ × 5.5″ | 19 × 140 mm | 1x Boards | 4.13 in² | N/A (Siding) |
| 1" × 8" | 0.75″ × 7.25″ | 19 × 184 mm | 1x Boards | 5.44 in² | N/A |
| 1" × 10" | 0.75″ × 9.25″ | 19 × 235 mm | 1x Boards | 6.94 in² | N/A (Shelving) |
| 1" × 12" | 0.75″ × 11.25″ | 19 × 286 mm | 1x Boards | 8.44 in² | N/A (Shelving) |
| 2" × 2" | 1.5″ × 1.5″ | 38 × 38 mm | 2x Dimension | 2.25 in² | N/A (Baluster) |
| 2" × 3" | 1.5″ × 2.5″ | 38 × 64 mm | 2x Dimension | 3.75 in² | N/A (Framing) |
| 2" × 4" | 1.5″ × 3.5″ | 38 × 89 mm | 2x Dimension | 5.25 in² | 6' - 8" |
| 2" × 6" | 1.5″ × 5.5″ | 38 × 140 mm | 2x Dimension | 8.25 in² | 9' - 9" |
| 2" × 8" | 1.5″ × 7.25″ | 38 × 184 mm | 2x Dimension | 10.88 in² | 12' - 10" |
| 2" × 10" | 1.5″ × 9.25″ | 38 × 235 mm | 2x Dimension | 13.88 in² | 16' - 2" |
| 2" × 12" | 1.5″ × 11.25″ | 38 × 286 mm | 2x Dimension | 16.88 in² | 19' - 6" |
| 4" × 4" | 3.5″ × 3.5″ | 89 × 89 mm | 4x Timber | 12.25 in² | N/A (Post: max 8ft high) |
| 4" × 6" | 3.5″ × 5.5″ | 89 × 140 mm | 4x Timber | 19.25 in² | Beam: Up to 8ft span |
| 6" × 6" | 5.5″ × 5.5″ | 140 × 140 mm | Heavy Timbers | 30.25 in² | Post: Up to 14ft high |
| 8" × 8" | 7.5″ × 7.5″ | 191 × 191 mm | Heavy Timbers | 56.25 in² | Heavy Column |
Why Is Actual Lumber Smaller Than Nominal Size?
When lumber is first cut from a raw log at the sawmill, it is cut to its full rough dimensions (e.g., a rough 2x4 is literally 2 inches by 4 inches of green wood). However, two subsequent manufacturing steps reduce its final dimensions:
- Kiln Drying: Green wood contains high moisture content (often >30%). Lumber is kiln-dried down to 15% to 19% moisture to prevent warping, which naturally shrinks the wood grain.
- Planing (Surfaced 4 Sides — S4S): To make the rough wood smooth, uniform, and safe to handle without splinters, high-speed planers shave down all four sides, removing approximately 1/4″ to 1/2″ of material.
Rules of Thumb for Converting Nominal to Actual Dimensions
- Nominal vs Actual Rule (Width & Thickness under 6″): Subtract 1/2″ (0.5″) from the nominal size (e.g., 2×4 becomes 1.5″ × 3.5″; 4×4 becomes 3.5″ × 3.5″).
- Nominal vs Actual Rule (Width 6″ and larger): Subtract 3/4″ (0.75″) from the nominal width (e.g., 2×6 becomes 1.5″ × 5.5″; 2×8 becomes 1.5″ × 7.25″; 2×10 becomes 1.5″ × 9.25″; 2×12 becomes 1.5″ × 11.25″).
- 1x Board Rule: All 1x nominal boards (1x2 through 1x12) have a finished actual thickness of 3/4″ (0.75″ or 19 mm).
- Metric Rule: Millimeters are based on the standard soft conversion: 1.5″ = 38 mm, 3.5″ = 89 mm, 5.5″ = 140 mm, 7.25″ = 184 mm, 9.25″ = 235 mm, 11.25″ = 286 mm.
How to Calculate Board Feet (BF)
Lumber volume in commercial trade is measured in Board Feet (BF). One board foot represents a volume of 1 square foot of lumber that is 1 inch thick nominal (144 cubic inches).
Board Feet = (Nominal Thickness in inches × Nominal Width in inches × Length in feet) ÷ 12 For a 12-foot long 2x8 board: (2 in × 8 in × 12 ft) ÷ 12 = 16.0 Board Feet (BF). Notice that nominal dimensions are used for volume calculations in the lumber trade.
Lumber Weight by Wood Species
The weight of dimensional lumber depends on the wood species density and moisture content. For standard kiln-dried lumber at approximately 15% moisture content:
- Southern Yellow Pine (SYP): ~37 lbs/cu.ft (Heaviest soft framing lumber; high structural strength).
- Douglas Fir / Larch: ~34 lbs/cu.ft (Standard West Coast framing timber).
- Spruce-Pine-Fir (SPF): ~28 lbs/cu.ft (Lightweight general construction framing).
- Pressure-Treated Pine: ~46 to 55 lbs/cu.ft (Contains chemical water preservative; wet from treatment).
- Western Red Cedar / Redwood: ~23 to 28 lbs/cu.ft (Naturally rot-resistant exterior timber).
Frequently Asked Questions About Lumber Sizes
Why is a 2x4 not 2 inches by 4 inches?
A 2x4 is not 2″ × 4″ because of the shrinkage and planing process at sawmills. The 'nominal' 2×4 size is the rough, green lumber dimension cut straight from the log. After being kiln-dried (which shrinks the fibers) and surfaced smooth on all four sides (S4S planing), it finishes at an actual size of 1-1/2″ × 3-1/2″ (38 × 89 mm).
What is nominal vs actual lumber size?
Nominal size is the rough-sawn industry label used for identification and sales (e.g., 2×4, 2×6, 4×4). Actual size is the precise finished physical measurement after kiln drying and S4S (Surfaced 4 Sides) planing. As a standard rule: dimensional lumber under 6″ is 1/2″ smaller than nominal; lumber 6″ and wider is 3/4″ smaller; 1x boards are 1/4″ thinner (0.75″).
What is the actual size of a 2x4 and a 4x4?
The actual finished size of a 2x4 is 1-1/2″ × 3-1/2″ (1.5″ × 3.5″ / 38 × 89 mm). The actual finished size of a 4x4 post is 3-1/2″ × 3-1/2″ (3.5″ × 3.5″ / 89 × 89 mm).
What is the actual size of a 2x8 lumber board?
The actual finished size of a 2x8 lumber board is 1-1/2″ × 7-1/4″ (1.5″ × 7.25″ in decimals, or 38 mm × 184 mm in metric).
What are the actual sizes for 2x6, 2x10, and 2x12 lumber?
A 2x6 is actually 1-1/2″ × 5-1/2″ (38 × 140 mm). A 2x10 is actually 1-1/2″ × 9-1/4″ (38 × 235 mm). A 2x12 is actually 1-1/2″ × 11-1/4″ (38 × 286 mm).
What are standard lumber dimensions in millimeters (metric)?
Common dimensional lumber sizes converted to metric millimeters (actual finished S4S): 2x4 = 38 × 89 mm; 2x6 = 38 × 140 mm; 2x8 = 38 × 184 mm; 2x10 = 38 × 235 mm; 2x12 = 38 × 286 mm; 4x4 = 89 × 89 mm; 6x6 = 140 × 140 mm; 1x4 = 19 × 89 mm; 1x6 = 19 × 140 mm.
How do you calculate board feet (BF) for lumber?
To calculate Board Feet (BF), use the formula: (Nominal Thickness in inches × Nominal Width in inches × Length in feet) ÷ 12. For example, a 10-foot long 2x8 contains (2 × 8 × 10) / 12 = 13.33 Board Feet.
How much does a 10-foot 2x8 weigh?
A dry 10-foot 2x8 (Douglas Fir / Southern Yellow Pine at ~15% moisture content) weighs approximately 26 to 28 lbs (11.8 to 12.7 kg). If the 2x8 is fresh green or pressure-treated (wet), it can weigh between 35 and 45 lbs (15.8 to 20.4 kg).
How far can a 2x6, 2x8, and 2x10 span as floor joists?
Under standard IRC residential design loads (40 psf live load, 10 psf dead load, L/360 deflection, spaced 16″ on-center with #2 Southern Pine or Douglas Fir): a 2x6 spans up to 9′ - 9″; a 2x8 spans up to 12′ - 10″; a 2x10 spans up to 16′ - 2″; and a 2x12 spans up to 19′ - 6″.
What is the actual size of 1x boards (1x4, 1x6, 1x8, 1x10, 1x12)?
All 1x boards have an actual thickness of 3/4″ (0.75″ or 19 mm). The actual widths are: 1x4 is 3-1/2″ (89 mm); 1x6 is 5-1/2″ (140 mm); 1x8 is 7-1/4″ (184 mm); 1x10 is 9-1/4″ (235 mm); and 1x12 is 11-1/4″ (286 mm).