What Are the Actual Dimensions of a 2x4? Nominal vs Actual Lumber Sizes
By Vinay S · Updated October 13, 2026
A 2x4 is actually 1-1/2 inches by 3-1/2 inches (38 mm by 89 mm). The 2x4 name is the nominal size, a label that describes the board before it was dried and planed. Every piece of common dimension lumber follows the same pattern, so a 2x6 is really 1-1/2 by 5-1/2 and a 4x4 is really 3-1/2 by 3-1/2.
Use the chart below when you measure for a wall, a deck or a set of shelves.
Nominal vs actual sizes
These are the finished sizes of dry softwood dimension lumber. The 1x through 4x rows come from Inch Calculator’s chart. The 6x6 row follows the same half-inch rule, which Inch Calculator states for nominal sizes from 2 inches to under 8 inches.
| Nominal size | Actual size (inches) |
|---|---|
| 1x2 | 3/4 x 1-1/2 |
| 1x4 | 3/4 x 3-1/2 |
| 1x6 | 3/4 x 5-1/2 |
| 1x8 | 3/4 x 7-1/4 |
| 1x10 | 3/4 x 9-1/4 |
| 1x12 | 3/4 x 11-1/4 |
| 2x2 | 1-1/2 x 1-1/2 |
| 2x4 | 1-1/2 x 3-1/2 |
| 2x6 | 1-1/2 x 5-1/2 |
| 2x8 | 1-1/2 x 7-1/4 |
| 2x10 | 1-1/2 x 9-1/4 |
| 2x12 | 1-1/2 x 11-1/4 |
| 4x4 | 3-1/2 x 3-1/2 |
| 4x6 | 3-1/2 x 5-1/2 |
| 6x6 | 5-1/2 x 5-1/2 |
Notice that boards 8 inches wide and over lose 3/4 inch instead of 1/2 inch. That is why a 2x8 is 7-1/4 and not 7-1/2.
Why a 2x4 shrinks
Two things happen between the log and the lumber yard.
Drying comes first. Fresh-cut wood holds a lot of water, and it shrinks as that water leaves. SPIB, the Southern Pine Inspection Bureau, explains that the nominal name refers to the wood size before it has been planed smooth and squared on all four sides, and that some shrinkage also happens as the wood dries.
Planing comes second. The mill runs each board through a planer so all four faces are flat and smooth. That removes more wood.
Today the sawmill plans for both losses. Inch Calculator says boards are intentionally cut large to allow for shrinkage during kiln drying and milling. The finished size is the same from mill to mill.
The standard behind it
In the United States, the sizes are set by the American Softwood Lumber Standard, known as PS 20, published through the National Institute of Standards and Technology. The Southern Pine council notes that PS 20 ties lumber size to moisture content, with separate size schedules for green and dry lumber so that both end up close to the same size in service.
Dry lumber is lumber seasoned to a moisture content of 19% or less. Most framing lumber you buy at a home center is sold dry, which is why the chart above applies to it. Green lumber is cut larger because it has more shrinking left to do.
Stud lengths: 92-5/8 and 104-5/8
Length is a separate story. A board sold as 8 ft is 96 inches long, and a 10 ft board is 120 inches. The exception is the precut stud.
A precut stud for an 8 ft wall is 92-5/8 inches. For a 9 ft wall it is 104-5/8 inches. The studs are shorter than the wall because the wall has plates. The math for an 8 ft wall looks like this.
| Part | Math | Height |
|---|---|---|
| Bottom plate | 1 x 1-1/2 | 1-1/2 in |
| Precut stud | 92-5/8 in | |
| Two top plates | 2 x 1-1/2 | 3 in |
| Framed wall | 1-1/2 + 92-5/8 + 3 | 97-1/8 in |
For a 9 ft wall the same math gives 1-1/2 + 104-5/8 + 3 = 109-1/8 inches.
The framed wall ends up 1-1/8 inches taller than 96 inches. Fine Homebuilding quotes framer Mike Guertin saying that studs precut to 92-5/8 leave a gap of 1/2 to 7/8 inch at the bottom of the wall once the drywall is up. That gap keeps the drywall sheets from sitting on the floor, and baseboard covers it.
You can plan your wall in the Stud Calculator, which counts studs for a wall length and spacing.
A worked example
Say you are framing a 12 ft wall with studs 16 inches on center. The studs are 1-1/2 inches thick.
- The wall is 12 ft x 12 = 144 inches long.
- At 16 inches on center, you need 144 / 16 = 9 spaces, so 9 + 1 = 10 studs.
- Add extra studs for any corner or opening in the wall.
The plates run the full 144 inches, and each one is a 2x4 that is 3-1/2 inches wide. Using the actual width matters when you cut drywall or trim to fit against the plate.
Now a board-foot example. A buyer asks for the volume in board feet of one 8 ft 2x4. A board foot is 144 cubic inches. The nominal math (2 x 4 x 96) / 144 = 5.33 board feet. Lumber is sold by nominal size, so the yard prices it as 5.33 board feet even though the real volume is smaller: (1.5 x 3.5 x 96) / 144 = 3.5 board feet. The Board Foot Calculator lets you check either number.
Tips for measuring
Measure the actual board before you cut. Dry lumber varies slightly, and a damp board may still be a little bigger. If you build to a nominal size on paper, your frame comes out short by the difference. For instance, three 2x4s side by side on a flat measure 3 x 3-1/2 = 10-1/2 inches, not 12.
Sources
Frequently asked questions
What are the actual dimensions of a 2x4?
1-1/2 inches by 3-1/2 inches (38 mm by 89 mm). The 2x4 name is the nominal size, which describes the board before it was dried and planed.
Why is a 2x4 not 2 inches by 4 inches?
The board was cut close to 2 by 4 inches when green, then it shrank as it dried and lost more wood when the mill planed it smooth. Inch Calculator says boards are now cut oversize on purpose so they finish at the standard size.
How long is a precut stud?
A precut stud for an 8 ft wall is 92-5/8 inches. For a 9 ft wall it is 104-5/8 inches. With a bottom plate and two top plates (3 x 1-1/2 inches = 4-1/2 inches), the framed wall is 97-1/8 inches or 109-1/8 inches tall.
Is a 4x4 really 4 inches by 4 inches?
A 4x4 post is 3-1/2 inches by 3-1/2 inches. Nominal sizes from 2 inches up to under 8 inches run about 1/2 inch smaller, so a 6x6 is normally 5-1/2 inches by 5-1/2 inches.
Is the length of a 2x4 also smaller than its label?
No. Length is not trimmed the way thickness and width are. An 8 ft 2x4 is sold as a board 96 inches long, and precut studs are the exception because the mill cuts them shorter on purpose.
Do I use nominal or actual size for a project?
Use actual size for anything you measure or cut, such as stud spacing, joist hangers, post bases and board-foot math. Use nominal size only when you order lumber at the yard.