Actual Lumber Sizes Chart
Complete guide to actual vs nominal lumber dimensions. Learn the real sizes of 2x4s, 2x6s, 4x4 posts, and all dimensional lumber for accurate project planning.
Quick Answer
Lumber sizes refer to rough-sawn dimensions before drying and planing. After processing, lumber is approximately 1/2" smaller in each dimension. Here are the most common sizes:
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Table of Contents
Lumber Size Charts
1× Lumber (Boards)
1-by boards are commonly used for shelving, trim, siding, and light carpentry. All 1× lumber is actually 3/4" (0.75") thick.
| Nominal Size | Actual Size (Inches) | Actual Size (Decimal) | Metric (mm) |
|---|---|---|---|
| 1×2 | 3/4" × 1-1/2" | 0.75" × 1.5" | 19 × 38 mm |
| 1×3 | 3/4" × 2-1/2" | 0.75" × 2.5" | 19 × 64 mm |
| 1×4 | 3/4" × 3-1/2" | 0.75" × 3.5" | 19 × 89 mm |
| 1×6 | 3/4" × 5-1/2" | 0.75" × 5.5" | 19 × 140 mm |
| 1×8 | 3/4" × 7-1/4" | 0.75" × 7.25" | 19 × 184 mm |
| 1×10 | 3/4" × 9-1/4" | 0.75" × 9.25" | 19 × 235 mm |
| 1×12 | 3/4" × 11-1/4" | 0.75" × 11.25" | 19 × 286 mm |
2× Lumber (Dimensional)
2-by lumber is the most common framing lumber. All 2× lumber is actually 1-1/2" (1.5") thick.
| Nominal Size | Actual Size (Inches) | Actual Size (Decimal) | Metric (mm) |
|---|---|---|---|
| 2×2 | 1-1/2" × 1-1/2" | 1.5" × 1.5" | 38 × 38 mm |
| 2×3 | 1-1/2" × 2-1/2" | 1.5" × 2.5" | 38 × 64 mm |
| 2×4 | 1-1/2" × 3-1/2" | 1.5" × 3.5" | 38 × 89 mm |
| 2×6 | 1-1/2" × 5-1/2" | 1.5" × 5.5" | 38 × 140 mm |
| 2×8 | 1-1/2" × 7-1/4" | 1.5" × 7.25" | 38 × 184 mm |
| 2×10 | 1-1/2" × 9-1/4" | 1.5" × 9.25" | 38 × 235 mm |
| 2×12 | 1-1/2" × 11-1/4" | 1.5" × 11.25" | 38 × 286 mm |
| 2×14 | 1-1/2" × 13-1/4" | 1.5" × 13.25" | 38 × 337 mm |
4× Lumber (Posts & Beams)
4-by lumber is used for posts, beams, and structural applications. All 4× lumber is actually 3-1/2" (3.5") in the first dimension.
| Nominal Size | Actual Size (Inches) | Actual Size (Decimal) | Metric (mm) |
|---|---|---|---|
| 4×4 | 3-1/2" × 3-1/2" | 3.5" × 3.5" | 89 × 89 mm |
| 4×6 | 3-1/2" × 5-1/2" | 3.5" × 5.5" | 89 × 140 mm |
| 4×8 | 3-1/2" × 7-1/4" | 3.5" × 7.25" | 89 × 184 mm |
| 4×10 | 3-1/2" × 9-1/4" | 3.5" × 9.25" | 89 × 235 mm |
| 4×12 | 3-1/2" × 11-1/4" | 3.5" × 11.25" | 89 × 286 mm |
6× Lumber (Heavy Timber)
6-by lumber is used for heavy-duty posts, beams, and timber frame construction. All 6× lumber is actually 5-1/2" (5.5") in the first dimension.
| Nominal Size | Actual Size (Inches) | Actual Size (Decimal) | Metric (mm) |
|---|---|---|---|
| 6×6 | 5-1/2" × 5-1/2" | 5.5" × 5.5" | 140 × 140 mm |
| 6×8 | 5-1/2" × 7-1/2" | 5.5" × 7.5" | 140 × 191 mm |
| 6×10 | 5-1/2" × 9-1/2" | 5.5" × 9.5" | 140 × 241 mm |
| 6×12 | 5-1/2" × 11-1/2" | 5.5" × 11.5" | 140 × 292 mm |
8× Lumber (Heavy Timber)
8-by lumber is used for major structural beams, posts, and timber frame construction.
| Nominal Size | Actual Size (Inches) | Actual Size (Decimal) | Metric (mm) |
|---|---|---|---|
| 8×8 | 7-1/2" × 7-1/2" | 7.5" × 7.5" | 191 × 191 mm |
| 8×10 | 7-1/2" × 9-1/2" | 7.5" × 9.5" | 191 × 241 mm |
| 8×12 | 7-1/2" × 11-1/2" | 7.5" × 11.5" | 191 × 292 mm |
Why Nominal and Actual Sizes Differ
The difference between nominal and actual lumber sizes dates back to when lumber was sold in its rough-sawn state. The nominal size represents the dimensions before drying and planing.
The Lumber Processing Journey
- 1. Rough Sawing: Logs are cut to nominal dimensions (e.g., 2" × 4")
- 2. Drying: Wood shrinks as moisture content drops from 30%+ to 15-19% (air-dried) or 6-12% (kiln-dried). This causes ~1/4" shrinkage.
- 3. Planing: Surfaces are planed smooth, removing another ~1/4" from each dimension
- 4. Final Size: The result is approximately 1/2" smaller in each dimension
Note on Larger Timbers
Lumber 5" and larger (like 6×6 and 8×8) loses only 1/2" total from each dimension rather than per side, making them closer to nominal. This is because they are often sold partially air-dried or "green."
Understanding Dimensional Lumber
Dimensional lumber is wood that has been cut to standardized sizes. It's the most common type of lumber used in construction and is available at any home improvement store.
Softwood Lumber
Most dimensional lumber is softwood (pine, spruce, fir). It's lightweight, affordable, and easy to work with. Common species include SPF (Spruce-Pine-Fir), Douglas Fir, and Southern Yellow Pine.
Hardwood Lumber
Hardwood (oak, maple, walnut) is sold by actual dimensions or "board feet" rather than nominal sizes. It's used for furniture, cabinetry, and trim work.
Pressure-Treated Lumber
Treated lumber uses the same nominal sizing. Common sizes include 2×4, 2×6, 4×4, and 6×6 for decks, fences, and outdoor structures.
Engineered Lumber
LVL, I-joists, and glulam beams often use different sizing conventions. Always check specifications for actual dimensions.
Common Uses for Each Size
| Size | Common Applications |
|---|---|
| 2×4 | Wall studs, light framing, furring strips, interior non-load bearing walls |
| 2×6 | Exterior walls, floor joists (short spans), deck framing, load-bearing walls |
| 2×8 | Floor joists, rafters, headers, deck beams |
| 2×10 | Floor joists (longer spans), rafters, stair stringers |
| 2×12 | Floor joists (long spans), ridge beams, stair stringers, headers |
| 4×4 | Deck posts, fence posts, porch columns, light structural posts |
| 6×6 | Heavy deck posts, porch posts, pergola posts, structural beams |
Tips for Buying Lumber
1. Measure Twice
When planning projects, always use actual dimensions. If you need a 4" wide piece, you'll need a 1×6 (actually 5.5") since a 1×4 is only 3.5" wide.
2. Check for Straightness
Sight down the length of each board. Avoid warped, twisted, or bowed lumber. Stack the board flat and check if it lies flat.
3. Inspect for Defects
Check for large knots, splits, checks (cracks), and excessive sapwood. Some defects are acceptable for framing but not for visible applications.
4. Understand Lumber Grades
Construction grade (stud, #2, #3) is fine for framing. Select or appearance grade is needed for visible projects. Pressure-treated comes in different retention levels for ground contact vs. above-ground use.
Frequently Asked Questions
What is the actual size of a 2×4?
A 2×4 actually measures 1-1/2 inches by 3-1/2 inches (1.5" × 3.5"). The nominal name "2×4" refers to the rough-sawn dimensions before drying and planing.
Why are lumber sizes different from their names?
Lumber is named by its rough-sawn dimensions before drying and planing. During processing, approximately 1/2 inch is removed from each dimension through shrinkage and surfacing, making a 2×4 actually 1.5" × 3.5".
What is the actual size of a 2×6?
A 2×6 actually measures 1-1/2 inches by 5-1/2 inches (1.5" × 5.5"). Like all dimensional lumber, it loses about 1/2 inch from each dimension during the drying and planing process.
What is the actual size of a 4×4 post?
A 4×4 post actually measures 3-1/2 inches by 3-1/2 inches (3.5" × 3.5"). It is 1/2 inch smaller than its nominal size in each dimension.
Are dimensional lumber sizes the same everywhere?
In North America, dimensional lumber follows standardized sizes. However, lumber in other countries may use metric dimensions or have different standards. Always verify sizes when purchasing imported lumber.
Is rough-sawn lumber full size?
Yes, rough-sawn lumber (also called "rough-cut" or "full-dimension") is sold at its nominal size. A rough-sawn 2×4 is actually 2" × 4". It's commonly used for rustic projects and is available at sawmills.
Related Resources
Dr. Snezana Lawrence
Mathematical Historian | PhD from Yale
Dr. Lawrence is a published mathematical historian with a PhD from Yale University. She ensures mathematical precision and accuracy in all our calculations, conversions, and academic score calculators. Her expertise spans computational mathematics and educational assessment.
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