Basic lumber dimensions are not as basic to many people as you might think they are. I get asked about actual lumber dimensions on a regular basis. Most people know that a 2×4 is actually 1.5″x3.5″ but the measurements get a little hazy with the large boards like 2×8’s and 2×12’s.
Lumber Dimensions
Here is a simple chart to clear up the confusion about 1x, 2x, and 4x nominal lumber dimensions versus actual lumber dimensions. The chart also includes the equivalent metric lumber dimensions. This chart applies to treated and untreated pine construction grade lumber.
This chart applies to the lumber dimensions of “quarter” measurements. The nominal dimensions are said as “five-quarter by four” or “six-quarter by six” etc. These are not all that common but you can usually find “five-quarter” decking whose actual dimension is 1″x5.5″.
Timber Dimensions
Lumber cut 5 inches or thicker is generally classified as timbers. Timbers are usually cut “rough” to actual dimensions. In other words, what you see is what you get. A 6×6 is 6″x6″, a 10×10 is 10″x10″ and so forth.
Post Dimensions
Round stock dimensions can get a little complicated but we will keep it simple here. A thorough discussion including large poles requires getting into the differences between poles and pilings and classes of utility poles and what you are using them for and it goes on and on so…so for the purpose of this article, I will stick to small posts.
Small posts are usually measured by the top size (the little end). So, if you want a 4″ top x 8′ long fence post, you would ask for a “four inch - eight” post. The line between posts and poles is a fuzzy one but after about ten or twelve feet long, whatever it is that you want usually become a pole. If you are using it in water to support a structure it is probably a piling, which is used upside down and measured by the butt (the big end)… and see how it easy it is to get complicated when discussing poles?
If you want square posts make sure you are clear about that when you ask for “posts”.
Lumber Dimensions Questions?
If you have any questions about lumber dimensions, let me know with a comment. I am always happy to help.
This entry was posted on Friday, February 15th, 2008 at 5:15 pm and is filed under Treated Wood, Specs & Data. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
what would be the nominal size of 8×8, I am building on the river and the company doing the no-rise certoficate asked “what is the nominal size of the timber piles for the dock and the house we are using 8×8 on the house and the dock except for tthe two pieces hold the floating dock what does he mean?
Marvin,
I am not sure they asked you the right question but big timbers like 8×8’s usually come in full-rough dimensions.
So, an 8×8 is usually actually 8″ by 8″. It is the milling process that makes the actual dimensions of a board smaller but big timbers typically retain their full size.
However, if you are using S4S (smooth 4 sides) and the timbers were planed, they are probably something more like 7.5″ by 7.5″.
Thanks for visiting Lumber Talk!
Chris