Why Your Lumber Isn’t The Size Listed On The Label & How To Measure Accurately

Have you ever gone to purchase wood for a project, you have all the measurements you need, purchase what you calculated and then get home only to find out that the lumber isn’t the size it says it is on the sticker? Well, you’re not alone. We’ve all been there and in this article I am going to explain WHY wood isn’t the size it says it is on the sticker.

Dimensional Lumber

Lumber is measured in different metrics. When you purchase wood from places like Lowe’s and Home Depot, you are purchasing what is called “dimensional” lumber. This means that they post the “nominal” size on the label, but the actual size is smaller. The nominal size is the size of the lumber before the mill planed the boards down smooth. This usually takes anywhere from .25-.50 inches off of each side. The chart below shows common nominal vs actual sizes.

Nominal Size	Actual Size
1 x 2	.75″ x 1.5″
1 x 3	.75″ x 2.5″
1 x 4	.75″ x 3.5″
1 x 6	.75″ x 5.5″
1 x 8	.75″ x 7.25″
1 x 10	.75″ x 9.25″
1 x 12	.75″ x 11.25″
2 x 2	1.5″ x 1.5″
2 x 3	1.5″ x 2.5″
2 x 4	1.5″ x 3.5″
2 x 6	1.5″ x 5.5″
2 x 8	1.5″ x 7.25″
2 x 10	1.5″ x 9.25″
2 x 12	1.5″ x 11.25″

These measurements only apply to lumber you purchase from stores such as Lowe’s and Home Depot.

Quarters Sizing

Whenever you go to an actual lumber yard they will have a different process for measuring their boards. Most lumber yards use “quarters” sizing. This is the true measurement of the boards BEFORE they get planed smooth. So when you purchase from a lumber yard, most times the wood you will get will be rough cut and not smooth. Most woodworkers prefer this as we can mill the wood ourselves to get the exact thickness and widths we need. The chart below explains how the quarters sizing works.

Quarter Size (thickness)	Actual Size (thickness)
4/4	1″
5/4	1.25″
6/4	1.5″
8/4	2″
10/4	2.5″
12/4	3″

S4S or “Surfaced on 4 Sides” Sizing

Lastly there is S4S lumber sizing. This measurement is mostly used by lumber yards as well. If you need your boards milled by the lumber yard because you do not have the milling tools at home (jointer and planer), they will charge an additional fee to plane them smooth for you on all 4 sides. Hence the term “S4S’ which stands for “Surfaced on 4 Sides”. Most dimensional lumber you purchase from the hardware stores will already be S4S which is why the measurements on the labels are bigger than the actual size of the boards. Because you are purchasing a rough 2×4 that has been surfaced on all 4 sides so it is now 1.5″ x 3.5″.

Calculating Lumber Prices

The last thing I will speak about in this article is how to calculate board feet. You will notice how most pine at the hardware stores are priced per board. While others such as the red oak, poplar, and other hardwoods are priced by the linear foot. Then, if you go to a lumber yard, they will charge by the board foot.

To calculate linear foot pricing you simply multiply the length of the board in feet by the price per foot to get the price for the entire board. Ex: a 10′ board that’s $5/lf would cost you $50.

Length of board x price per foot = total cost for that board

Board foot pricing is much trickier and took me a while to understand. You must calculate the length of the board as well as the thickness and width. The easiest way I have found to do this is to do so in inches. So if you had that same 10′ long board and it was 10″ wide and 2″ thick- you would multiply 120″ x 10″ x 2″ which comes to 2400. Then to get the board foot calculation you will divide that number by 144 (which is 12×12 or a foot x a foot) so 2400/144 will leave you with 16.67 board feet. If the price per board foot is $5, then that brings your total for the one board to $83.33.

Length of board x thickness x width (all in inches) ÷ 144 = Board feet for that board

Board foot calculation x price per board foot = total cost for that board

I hope this article has helped you better understand how lumber is calculated and sized/marked! If you have any questions, don’t hesitate to reach out on my instagram! I am an open book and love engaging with my followers!