2×4 Nominal Size vs Actual Size
What is the nominal size?
The nominal size is the name given to a piece of lumber based on its rough-cut dimensions. A 2×4 starts out close to 2 inches thick and 4 inches wide when first cut from the log. These measurements are taken **before** the wood is dried and surfaced.
What is the actual size?
The actual size is the finished measurement after the board is kiln-dried and planed smooth. This process reduces the thickness and width, producing the consistent 1.5″ × 3.5″ size you find at most lumberyards.
Nominal vs actual size table
| Type | Nominal Size | Actual Size (Inches) | Actual Size (Metric) |
|---|---|---|---|
| Standard kiln-dried 2×4 | 2″ × 4″ | 1.5″ × 3.5″ | 38 × 89 mm |
| Green/rough 2×4 | 2″ × 4″ | 1.75″ × 3.75″ | 44 × 95 mm |
Why the difference matters
Knowing the difference between nominal and actual size is essential for accurate project planning. If you design a frame based on the nominal size without adjusting, your cuts will be short.
FAQ
Is this difference unique to 2×4 lumber?
No. All dimensional lumber in North America has a nominal size and a smaller actual size.
Do other countries have the same difference?
Many countries using metric measurements follow a similar system where rough-sawn sizes are larger than finished sizes.