Nominal vs Actual Lumber Sizes
A 2×4 does not measure 2 inches by 4 inches. Its nominal size is the name it is sold under, and its actual size is what a tape measure reads: 1 1/2 inches by 3 1/2 inches. This page lists the actual size of common softwood lumber, explains where the difference comes from, and shows which set of numbers belongs in a board foot calculation.
Nominal vs Actual Lumber Sizes Chart
These are the dry dressed sizes for surfaced softwood lumber sold in the United States.
Nominal size | Actual size (inches) |
1×2 | 3/4 x 1 1/2 |
1×3 | 3/4 x 2 1/2 |
1×4 | 3/4 x 3 1/2 |
1×6 | 3/4 x 5 1/2 |
1×8 | 3/4 x 7 1/4 |
1×10 | 3/4 x 9 1/4 |
1×12 | 3/4 x 11 1/4 |
2×2 | 1 1/2 x 1 1/2 |
2×3 | 1 1/2 x 2 1/2 |
2×4 | 1 1/2 x 3 1/2 |
2×6 | 1 1/2 x 5 1/2 |
2×8 | 1 1/2 x 7 1/4 |
2×10 | 1 1/2 x 9 1/4 |
2×12 | 1 1/2 x 11 1/4 |
4×4 | 3 1/2 x 3 1/2 |
4×6 | 3 1/2 x 5 1/2 |
6×6 | 5 1/2 x 5 1/2 |
This nominal vs actual lumber sizes chart covers the boards most stores stock.
Lengths are not reduced. An 8 foot board is 8 feet long, and many mills cut it slightly over.
The Pattern Behind the Numbers
The chart follows three simple rules for dry lumber.
Nominal dimension | Dry dressed size | Amount removed |
1 inch | 3/4 inch | 1/4 inch |
2 to 6 inches | 1 1/2 to 5 1/2 inches | 1/2 inch |
8 inches and wider | 7 1/4 inches and up | 3/4 inch |
A 2×10 therefore loses 1/2 inch of thickness and 3/4 inch of width, which gives 1 1/2 by 9 1/4 inches.
Why Lumber Is Smaller Than Its Name
The nominal size goes back to the rough green board that came off the saw. Two things happen after that cut.
- Drying. Wood shrinks in thickness and width as it loses moisture. Lumber sold as dry has a moisture content of 19 percent or less.
- Surfacing. The mill planes all four sides smooth, which removes more wood.
The finished sizes are not left to each mill. They are set by Voluntary Product Standard PS 20, the American Softwood Lumber Standard, which lists a minimum dressed size for every nominal size. Lumber surfaced while still green is allowed to be slightly larger, for example 1 9/16 inches thick for a 2 inch nominal board, because it will shrink as it dries.
Which Size to Use for Board Feet
Softwood lumber is sold on nominal dimensions. When a yard quotes board feet for framing lumber, it multiplies the nominal thickness and width by the actual length. Use nominal numbers in the board foot calculator to match a supplier’s tally, and use actual numbers only when you need the true volume of wood, for example to estimate weight.
The table shows how far the two figures are apart.
Piece | Board feet sold (nominal) | Actual wood volume (board feet) | Actual as share of nominal |
2x4x8 | 5.33 | 3.50 | 66% |
2x6x8 | 8.00 | 5.50 | 69% |
2x8x10 | 13.33 | 9.06 | 68% |
2x10x12 | 20.00 | 13.88 | 69% |
2x12x16 | 32.00 | 22.50 | 70% |
4x4x8 | 10.67 | 8.17 | 77% |
The board foot chart lists nominal board feet for more sizes and lengths.
Knowing nominal vs actual lumber sizes keeps both the cost estimate and the cut list correct.
Hardwood Works Differently
Hardwood lumber does not use the 2×4 naming system. Its thickness is stated in quarters of an inch, such as 4/4 or 8/4, and that figure describes the rough board before surfacing. Width is measured as it is, not rounded to a nominal size. Board feet are charged on the rough thickness, even when the board has already been planed. The hardwood lumber thickness guide gives the rough and surfaced size for each quarter thickness.
Tips for Planning With Actual Sizes
Use these tips when you plan a project around nominal vs actual lumber sizes:
- Design with actual dimensions. Three 2x4s stacked on edge measure 10 1/2 inches, not 12.
- Check decking and trim labels. A 5/4 x 6 softwood deck board is 1 inch by 5 1/2 inches.
- Measure pressure treated lumber before cutting. It is often sold wet and can be slightly oversize until it dries.
- Buy on nominal, build on actual. Use nominal sizes for cost and actual sizes for the cut list.
Frequently Asked Questions
Sources
American Lumber Standard Committee: PS 20 documents
Southern Pine Inspection Bureau: Nominal vs Actual Lumber Sizes