When you buy lumber, understanding lumber sizes can be very confusing. I discovered this when taking my first carpentry class and tried to take notes. As the teacher explained the different ways lumber sizes are used, I didn't know what to write down or which dimensions to use when.
To this day it boggles my mind that a 2 x 4 piece of lumber is only 1 1/2 x 3 1/2 inches, but it's not going to change so it's time to learn lumber sizes. The simple, non-technical explanation is that when you talk about lumber, you call it a “2 by 4” and when you measure it, you'll find the smaller dimensions.
- Nominal lumber size – is the size wood is when it's cut at the lumber mill.
- Dimensional lumber – is the size of wood when it's dried and planed.
- Software lumber dimensions – can generally be estimated as follows, for softwoods. Hardwoods have less moisture so they shrink less (click for their dimensional sizes).
- 1/4 inch less for pieces of lumber that are one inch
- For pieces between one and six inches, subtract 1/2 inch.
- With pieces more than six inches, subtract 3/4 of an inch.
Learn more about softwoods at Wikipedia.
Softwood Dimensional Lumber Sizes
Here is a table with the most common dimensional lumber sizes for softwoods. The dimensions are for the wood's thickness and width, and the boards are sold by the lineal (running) foot.
For hardwoods sold at Home Depot and Lowes, ones planed on all four sides (known as S4S, surfaced 4 sides), they are the dimensions as the softwood chart. When you buy hardwoods at an actual lumber yard, they sizes are different.
These sizes also don't apply to woods like MDF, particle board, plywood, OSB or LVL, which are manufactured and use actual sizes.
|Softwood Lumber Sizes (Thickness x Width)|
|Nominal Lumber Dimensions||Actual Lumber Dimensions|
|1 x 2 inches||3/4 in x 1 1/2 inches|
|1 x 3 inches||3/4 in x 2 1/2 inches|
|1 x 4 inches||3/4 in x 3 1/2 inches|
|1 x 6 inches||3/4 in x 5 1/2 inches|
|1 x 8 inches||3/4 in x 7 1/2 inches|
|1 x 10 inches||3/4 in x 9 1/2 inches|
|1 x 12 inches||3/4 in x 11 1/2 inches|
|2 x 2 inches||3/4 in x 1 1/2 inches|
|2 x 3 inches||1 1/2 in x 2 1/2 inches|
|2 x 4 inches||1 1/2 in x 3 1/2 inches|
|2 x 6 inches||1 1/2 in x 5 1/2 inches|
|2 x 8 inches||1 1/2 in x 7 1/2 inches|
|2 x 10 inches||1 1/24 in x 9 1/2 inches|
|2 x 12 inches||1 1/2 in x 11 1/2 inches|
|4 x 4 inches||3 1/2 in x 3 1/2 inches|
|4 x 6 inches||3 1/2 in x 5 1/2 inches|
|6 x 6 inches||5 1/2 in x 5 1/2 inches|
|8 x 8 inches||7 1/4 in x 7 1/4 inches|