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 Home > Critical Path > Calculating Board Feet
 Calculating Board Feet
CHAPTER 1, LESSON 3 of 3

GOAL: To understand how to determine the amount of lumber required for a project as generated by the parts listed in the material list.

Determining how much lumber to procure for a project can be a bit tricky. This is especially true if you are purchasing hardwood lumber, which is often sold in random widths and lengths. This lesson will provide a woodworker with the tools needed to confidently source and purchase lumber.

 The material list below lists all the parts included in the bookshelf at left. Using the formulas found in the text and the charts to do the calculations, the material list below indicates that the bookshelf will require just a bit over 14 BF of lumber.

Thickness is the key to board foot calculations.
1"-stock  (1 x width x  length)/144 = board feet
Example 1x 8" x 60" / 144 = 3.33-board feet

1/2"-stock (.5 x width x  length)/144 = board feet
Example .5 x 8" x 60 / 144 = 1.66-board feet

1-1⁄2"-stock (1.5 x width x  length)/144 = board feet
Example 1.5 x 8" x 60" / 144 = 5-board feet
Roughsawn Converted to Finished Thickness
8/4 Roughsawn Stock = 1-3⁄4" finished thickness

6/4 Roughsawn Stock = 1-1⁄4" finished thickness

5/4 Roughsawn Stock = 1" finished thickness

4/4 Roughsawn Stock = 3/4" finished thickness

3/4 Roughsawn Stock = 1/2" finished thickness
 Roughsawn English brown oak lumber (above), each piece numbered as it was sawn from the log.

Once you have a material list developed for a project, the next step is to determine how much lumber and of what sizes you will need to complete the project. Lumber is sold in a wide variety of forms.

Dimension lumber (2 x 4s, 4 x 4s, 2 x 12s, etc.) is generally softwood lumber.

Hardwood lumber can be found in dimension sizes, but is more commonly found in random widths and lengths. It is sold as roughsawn lumber and in variable surfacing options with letter and number codes: S2S (surfaced two sides), S3S (surfaced two sides with one straight edge rip), S4S, (surfaced four sides, which means that the two wide faces have been planed and the two edges have been straight line ripped).

Rough lumber is sold in multiples of 1/4" thicknesses. So 4/4 lumber (read as four-quarter lumber) is one-inch thick. With any rough lumber thickness, subtract 1/4" to determine the surfaced thickness of the stock. For example, 4/4 lumber will plane clean at 3/4" ... 5/4 lumber will clean up to 1" thick. This is a rule of thumb, but it is pretty dependable.

### Board Feet

Lumber is generally sold by the board foot (BF) or some variation of that standard (rockler.com sells in tenths of board feet (TBF), for example). Think of a  board foot of lumber as 1" thick, 12" wide and 12" long (which is essentially 144 square inches of 1" thick lumber). So a 1" thick board, 6" wide and 36" long would be 1.5 (1-1⁄2) board feet of stock. (Formula: {1"x 6" x 36"} / 144 = 1.5 board feet)

The thickness of the lumber is a key factor in figuring board feet. The 1" dimension is the base line from which everything else is figured. For example, if you are using 1/2" lumber, mulitply the width by .5, as shown in the chart above right. (3/4" surfaced lumber is considered 1" when calculating board feet because it is derived from 4/4 roughsawn lumber.)

Determining how many board feet of lumber you need for a project is just the first step. Next you need to examine the material list for pieces that have length requirements. For example, if there are table legs that need to be 42" long, or bed rails that need to be 90" long, you will need to select or order stock long enough to make those parts.

Another rule of thumb is that once you have figured out how many board feet of lumber you need for a project, you will need to add 20 to 30% for waste. So if your project requres 10BF, you would procure 13BF.