Nominal vs Actual Lumber Sizes, Explained
July 6, 2026
Grab a tape measure, run it across the face of a 2x4, and you get 3.5 inches. Not 4. Run it across the thickness and you get 1.5, not 2. Nobody lied to you at the lumberyard. That gap between the name and the measurement is the difference between nominal and actual size, and it trips up every new woodworker at least once.
Here is the short version. Nominal size is the name. Actual size is what you measure. And board feet, the way lumber gets priced and sold, are figured at the nominal size.
Why a 2x4 is really 1.5 x 3.5
A board starts life bigger. When a green 2x4 gets sawn from the log, it really is close to 2 by 4. Then it dries, which shrinks it, and then it runs through a planer to get those smooth, flat faces. Planing shaves material off all four sides.
By the time the board hits the shelf, it lost about a half inch off the thickness and width. The 2 became 1.5. The 4 became 3.5. The name stuck around from the rough-sawn stage, so we still call it a 2x4.
Length is the exception. An 8-foot board is actually 8 feet, sometimes a hair over. Only thickness and width get trimmed down.
The chart: nominal vs actual dimensions
Here are the common sizes you'll see stacked at any yard. Thickness and width are in inches.
| Nominal | Actual, decimal (thickness x width) | Actual, fractions | Actual, mm |
|---|---|---|---|
| 1x2 | 0.75 x 1.5 | 3/4 x 1-1/2 | 19 x 38 |
| 1x3 | 0.75 x 2.5 | 3/4 x 2-1/2 | 19 x 64 |
| 1x4 | 0.75 x 3.5 | 3/4 x 3-1/2 | 19 x 89 |
| 1x6 | 0.75 x 5.5 | 3/4 x 5-1/2 | 19 x 140 |
| 1x8 | 0.75 x 7.25 | 3/4 x 7-1/4 | 19 x 184 |
| 1x10 | 0.75 x 9.25 | 3/4 x 9-1/4 | 19 x 235 |
| 1x12 | 0.75 x 11.25 | 3/4 x 11-1/4 | 19 x 286 |
| 2x2 | 1.5 x 1.5 | 1-1/2 x 1-1/2 | 38 x 38 |
| 2x3 | 1.5 x 2.5 | 1-1/2 x 2-1/2 | 38 x 64 |
| 2x4 | 1.5 x 3.5 | 1-1/2 x 3-1/2 | 38 x 89 |
| 2x6 | 1.5 x 5.5 | 1-1/2 x 5-1/2 | 38 x 140 |
| 2x8 | 1.5 x 7.25 | 1-1/2 x 7-1/4 | 38 x 184 |
| 2x10 | 1.5 x 9.25 | 1-1/2 x 9-1/4 | 38 x 235 |
| 2x12 | 1.5 x 11.25 | 1-1/2 x 11-1/4 | 38 x 286 |
| 4x4 | 3.5 x 3.5 | 3-1/2 x 3-1/2 | 89 x 89 |
| 4x6 | 3.5 x 5.5 | 3-1/2 x 5-1/2 | 89 x 140 |
| 6x6 | 5.5 x 5.5 | 5-1/2 x 5-1/2 | 140 x 140 |
Two patterns make this easy to remember. Anything nominal 1-inch thick planes down to 0.75. Anything nominal 2-inch thick planes down to 1.5. And once a board is 8 inches wide or more, it loses 3/4 inch off the width instead of 1/2 inch.
For a deeper walkthrough of these dimensions and where they come from, the full board foot chart breaks it down further.
Actual size of every common board, one at a time
The chart above is faster to scan, but if you came here looking up one specific board, here is each one on its own.
Actual size of a 1x2: 3/4 by 1-1/2 inches. It is the smallest common stick at the yard and the one people most often assume is a true 1 by 2. It is not, and at that size the missing quarter inch is a third of the stated width.
Actual size of a 1x3: 3/4 by 2-1/2 inches. Common as furring strip and strapping.
Actual size of a 1x4: 3/4 by 3-1/2 inches. Same width as a 2x4, half the thickness. If a plan calls for a 4-inch-wide trim piece, a 1x4 will leave you a half inch short.
Actual size of a 1x6: 3/4 by 5-1/2 inches. The standard fence picket and the widest board still losing only 1/2 inch off the width.
Actual size of a 1x8: 3/4 by 7-1/4 inches. This is where the rule changes. From 8 inches nominal and up, the board loses 3/4 inch of width instead of 1/2.
Actual size of a 1x10: 3/4 by 9-1/4 inches. Common as a stair riser and shelving board.
Actual size of a 1x12: 3/4 by 11-1/4 inches. The widest standard softwood board, and a common shelf. Plan a 12-inch shelf around 11-1/4 and you will not be sanding a cabinet to fit.
Actual size of a 2x2: 1-1/2 by 1-1/2 inches. Usually a ripped-down stick rather than a sawn one.
Actual size of a 2x3: 1-1/2 by 2-1/2 inches. Cheap non-structural framing, common in garage partition walls.
Actual size of a 2x4: 1-1/2 by 3-1/2 inches. The one everybody learns first.
Actual size of a 2x6: 1-1/2 by 5-1/2 inches. Exterior walls, deck joists on short spans, and the standard deck board in its 5/4 cousin.
Actual size of a 2x8: 1-1/2 by 7-1/4 inches. First of the joists to drop to the 3/4-inch width rule.
Actual size of a 2x10: 1-1/2 by 9-1/4 inches. The workhorse floor joist and stair stringer.
Actual width of a 2x12: 11-1/4 inches, at 1-1/2 thick. This is the one people measure twice, because 11-1/4 feels a long way from 12. It is the same 3/4-inch rule as every board 8 inches and wider.
Actual size of a 4x4: 3-1/2 by 3-1/2 inches. Standard deck and fence post, and the same 3-1/2 face as a 2x4 on both sides.
Actual size of a 6x6: 5-1/2 by 5-1/2 inches. Heavy post stock for pergolas, carports, and taller deck framing.
Two cautions on all of these. Rough-sawn and green lumber has not been planed yet, so it measures closer to its nominal name; the chart above is for surfaced dry material, which is what a home center sells. And pressure-treated stock is often a hair over these numbers when it is still wet from treatment, then settles back down as it dries.
Why board feet use nominal size
This is the part that saves you money and confusion. A board foot is figured at the nominal dimensions, not the actual planed size. So a 2x4 counts as a full 2 by 4 when you run the numbers.
The formula is simple:
board feet = (thickness x width x length in inches) / 144
Run a standard 2x4x8. That's 8 feet, or 96 inches long.
(2 x 4 x 96) / 144 = 5.33 board feet
If you used the actual 1.5 x 3.5 instead, you'd get 3.5 board feet, and every price and tally in the country would be wrong. The whole trade agrees to price at nominal, so everyone's math lines up. For the full breakdown of that one board, including a length chart and how to total a framing order, see how many board feet are in a 2x4.
A few more to lock it in, all at nominal size:
| Board | Board feet |
|---|---|
| 1x6x8 | 4 |
| 1x4x8 | 2.67 |
| 1x12x8 | 8 |
| 4x4x8 | 10.67 |
That 1x6x8 works out clean: (1 x 6 x 96) / 144 = 4. The 4x4x8 is (4 x 4 x 96) / 144 = 10.67. Dimensional softwood at the big-box store often gets sold by the linear foot instead, but hardwood and anything sold rough gets priced by the board foot at nominal.
Hardwood plays by a different rule: the quarter system
Everything above is softwood, the framing lumber at the home center. Hardwood, the walnut and oak and maple sold at a specialty yard, gets measured a different way.
Hardwood thickness is quoted in quarters of an inch. A board called 4/4 (say it "four quarter") is nominally 1 inch thick. 5/4 is 1.25 inches, 6/4 is 1.5, and 8/4 is 2. That number is the rough-sawn thickness before surfacing, so a 4/4 board planed smooth on both faces lands around 13/16 of an inch, a little under the full inch, the same shrink-and-plane story as a 2x4.
Width is not rounded to standard names the way softwood is. Hardwood comes in random widths, whatever the log gave, and you pay by the board foot at the rough size. That is why a hardwood price looks different from a softwood one: you are buying actual measured volume, not a named stick. If you are pricing a project, run the rough thickness and width through the board foot calculator, and the hardwood price per board foot guide shows what the common species cost.
Plywood and sheet goods shrink too
Dimensional lumber is not the only thing sold under a rounded-off name. A sheet of "3/4-inch" plywood has never measured a true 3/4 inch, even before sanding was standardized.
Old-style CDX and shop-grade plywood commonly ran about 1/32 inch under nominal, so 3/4 came in around 23/32. Sanded hardwood plywood and modern metric-influenced imports often run further under, closer to 11/16 for a nominal 3/4 sheet. The pattern repeats down the lineup: nominal 1/2 inch plywood is commonly 15/32 or thinner, and nominal 1/4 inch is often closer to 7/32.
The reason is the same story as dimensional lumber: sanding removes material after the panel is pressed to its rough thickness, and the name sticks from before that step. It matters most when a plan calls for a groove or a dado sized to fit a sheet good exactly. Measure the actual panel before cutting the joint, the same rule that applies to framing lumber above.
Common questions
Why isn't a 2x4 actually 2 by 4 inches? It started at roughly 2 by 4 when it was rough-sawn and green. Drying shrank it and planing smoothed it, taking about half an inch off the thickness and width. The rough-stage name stuck, so the smooth 1.5 by 3.5 board is still called a 2x4.
What is the actual size of a 2x6? 1.5 by 5.5 inches. Every nominal 2-inch board planes down to 1.5 thick, and a 6-inch width loses half an inch.
What are the actual dimensions of a 2x8, 2x10, and 2x12? 1.5 by 7.25, 1.5 by 9.25, and 1.5 by 11.25. Once a board is 8 inches wide or wider, it loses 3/4 inch off the width instead of 1/2 inch, which is why the widths end in .25.
What is the actual size of a 1x2? 3/4 by 1-1/2 inches. Of all the common sizes, this is the one where the gap hurts most, because a quarter inch missing off a 2-inch stated width is a much bigger share than a half inch off a 2x12.
What is the actual size of a 1x4? 3/4 by 3-1/2 inches. It has the same width as a 2x4 and half the thickness, which is why a 1x4 works as trim over 2x4 framing.
What is the actual size of a 1x10? 3/4 by 9-1/4 inches. It is 8 inches nominal and wider, so it follows the 3/4-inch width rule rather than the 1/2-inch one.
What is the actual size of a 4x4? 3-1/2 by 3-1/2 inches. A nominal 4-inch face planes down the same half inch a 2x4's width does.
Is a board's length nominal too? No. Length is actual. An 8-foot board really is 8 feet, sometimes a touch over. Only thickness and width get trimmed.
Do rough-sawn boards match this chart? No. Rough-sawn lumber has not been planed, so it measures close to its nominal name. The chart on this page is for surfaced dry lumber, which is what a home center stocks. If you buy rough, measure it, because that extra material is real and you paid for it.
What are lumber sizes in millimeters? A 2x4 is 38 by 89 mm, a 2x6 is 38 by 140, and a 2x10 is 38 by 235. Those come straight from converting the actual inch sizes, which is why they look like odd numbers rather than round metric ones.
Do hardwood boards follow the same chart? No. Hardwood uses the quarter system for thickness (4/4, 5/4, 8/4) and random widths, and it is priced by the board foot at the rough size, not by named sticks like a 2x4.
Is 3/4-inch plywood really 3/4 inch thick? No. A nominal 3/4-inch sheet typically measures around 23/32 to 11/16 inch, depending on the manufacturer and whether it is sanded. The gap comes from the same sanding-after-pressing process that shrinks dimensional lumber below its named size.
Where this actually bites you
Two places. First, cut lists. If your plan calls for a 3.5-inch-wide piece and you buy a 1x4 expecting 4 inches, you're short a half inch. Design around actual sizes, buy by nominal names.
Second, pricing. When you compare a hardwood quote to a home-center 2x4, remember one is priced at nominal board feet and the other might be linear feet of a smaller actual board. If that split confuses you, the breakdown in board foot vs linear foot sorts it out.
Keep a size chart handy until the numbers stick, then you'll stop second-guessing every board you pick up.