The Shrinkage Factor
When you buy a "2x4" at a hardware store, it's not actually 2 inches by 4 inches. 2x4 is the nominal size (the size it was when it was first cut green).
The Actual Dimensions
After drying and planing, the wood shrinks and is smoothed down.
- 2x4 = 1.5" x 3.5"
- 1x6 = 0.75" x 5.5"
- 4x4 = 3.5" x 3.5"
Why It Matters
If you design a project using nominal dimensions, your measurements will be off by half an inch or more, ruining your build.
Key Takeaways
- Always design with actual dimensions
- "Dimensional Lumber" is usually what you find at stores
- Rough-cut lumber is closer to its nominal size