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Buying Wood & Lumber By Size

The dimensions of a piece of wood purchased at your local lumber yard may not be what you expect. In the lumber industry wood is measured when it is rough cut not after it has been milled.

rough cut lumber

Figure 1 - Rough cut lumber

Rough cut lumber, as shown in Figure 1, was used in situations where the appearance of the wood was not as important as its cost. The most common application of rough-cut lumber was as barn siding, a smooth finished surface was definitely not worth paying any additional money.

Very few lumber yards carry rough cut lumber any longer, hence when you ask for a 2 x 4, you will get a piece of lumber that was rough cut as 2 inches X 4 inches and milled to 1 1/2 inches X 3 1/2 inches.

Note: The milling of lumber does vary from area to area. In some cases you will find that a milled 2 x 4 is actually 1 5/8 inches x 3 5/8 inches. Although the variance does not make a difference on new projects, if you are using the lumber to replace or add to an existing project, the difference in size can create problems. Always double check the actual lumber size with a tape measure, before purchasing.

Table 1 provides the most current and common dimensions for wood.

Table 1 - Common Wood Sizes

Nominal Lumber Size (inches)

Actual Lumber Size (Inches)

1 x

1

3/4 x

3/4

2

1.5

3

2.5

4

3.5

6

5.5

8

7 1/4

10

9 1/4

12

11 1/4

2 x

2

1 1/2 x

1 1/2

3

2 1/2

4

3 1/2

6

5 1/2

8

7 1/4

10

9 1/4

12

11 1/4

4 x

 

4

3 1/2 x

 

3 1/2

6

5 1/2

6 x

6

5 1/2 x

5 1/2

8 x

8

7 1/4 x

7 1/4

A lot of lumber is sold in board feet.

A board foot is based on the rough cut size of the lumber.

A board foot is 144 cubic inches of lumber. As an example a piece of lumber, with a rough-cut size of 1 inch thick, 12 inches wide and 12 inches long would be 1 board foot, (1 x 12 x 12 ÷ 144 = 1).

If the board was 2 inches thick it would be 2 board feet, (2 x 12 x 12 ÷ 144 = 2). If the board was 1 inch thick, 12 inches wide and 24 inches long it would also be 2 board feet, (1 x 12 x 24 ÷ 144 = 2).

Additional information on the weight of lumber.

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