Board Feet Calcualtions
Rough Sawn Lumber Vs Dimensioned Lumber
Sawmills and Lumber Wholesalers use Board Feet as a unit of measurement throughout the United States and Canada because most of it is not turned into a finished product like you would find in your big box home centers or lumber yards. One board foot of Rough Sawn Thickness (RGH) of lumber is a piece that is 1onein. in Thickness by 12 in. in width and 12 in. in length. Why sell lumber in this way? Since trees are round and then sawn into boards, it's a fair way to calculate the volume of the board that you are buying. If you purchase a piece of dimensioned lumber (something that is already finished on four sides), the cost is already calculated plus the price of the rough-sawn board and the cost of finishing the surfaces on all four sides) and it's calculated using the linear foot.
Terms that you should know
What does 4/4, 5/4, 6/4, 8/4 mean?
When a board is cut, it's cut by the sawmill to produce the most lumber possible. The Standard of measurement is quarters of an inch or 4. The quarter is 1 in. 5/4 Quarter is 1-1/4 in. in thickness. If you go into the big box stores and purchase a piece of 4/4 or 1-inch board, it will be about 3/4 of an inch thick because surfacing has taken it from 4/4 down to 3/4. That's why it's been dimensioned or processed if you buy a 2x4 or 8/4x 12/4. It's now down to 1-1/2 x 3-1/2 inches.
How to Measure Lumber
| Rough Sawn | Surfaced Two Sides | |
|---|---|---|
| 4/4 | 1 in. | 13/16 in. |
| 5/4 | 1.25 in. | 1/1/16 in. |
| 6/4 | 1.5 in. | 1/15/16 in. |
| 8/4 | 2 in. | 1/13/16 in. |
Why Board Feet
Hardwood is sold in random widths and lengths, so measuring the volume is the fairest and most equitable way to calculate the cost. Dimensioned lumber and wood are sold by the piece or the linear foot.
Why Random Widths and Lengths
Peices that have just emerged from the sawmill are not processed into any particular size yet. You could often have a piece with a natural edge or the outside growth of the tree on one or both edges. Trees are naturally round and irregular. When maximizing the amount of usable wood that can be harvested from a log, sawmills cut it into boards that provide the maximum yield. That results in a variety of lengths and widths. You do the cutting, gluing, and shaping for your particular project.
- Widths= to the nearest quarter of an inch
- Lengths = to the nearest who inch
- Thickness = you don't measure; you use the rough thickness name
Board Feet Calculation Cheat Sheet
1 Board Foot = 144 cubic inches
Board Feet = Rough Sawn T(thickness) (RGH) (in inches) x W(width) (in inches) x L(length) (in inches) ÷ 144
A common mistake most people make in calculating board footage is forgetting to multiply by the Thickness.
4/4 multiply by 1
5/4 multiply by 1.25
6/4 multiply by 1.5
8/4 multiply by 2
| 4/4 | 4 in. | 5 in. | 6 in. | 7 in. | 8 in. | 9 in. | 10 in. | 11 in. | 12 in. | |
|---|---|---|---|---|---|---|---|---|---|---|
| 48 in. | 1.33 | 1.67 | 2 | 2.33 | 2.67 | 3 | 3.33 | 3.67 | 4 | |
| 60 in. | 1.67 | 2.08 | 2.5 | 2.92 | 3.33 | 3.75 | 4.17 | 4.58 | 5 | |
| 72 in. | 2 | 2.5 | 3 | 3.5 | 4 | 4.5 | 5 | 5.5 | 6 | |
| 96 in. | 2.67 | 3.33 | 4 | 4.67 | 5.33 | 6 | 6.67 | 7.33 | 8 | |
| 120 in. | 3.33 | 4.17 | 5 | 5.83 | 6.67 | 7.5 | 8.33 | 9.17 | 10 | |
| 144 in. | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | |
| 5/4 | 4 in. | 5 in. | 6 in. | 7 in. | 8 in. | 9 in. | 10 in. | 11 in. | 12 in. | |
| 48 in. | 1.67 | 2.08 | 2.5 | 2.92 | 3.33 | 3.75 | 4.17 | 4.58 | 5 | |
| 60 in. | 2.08 | 2.6 | 3.13 | 3.65 | 4.17 | 4.69 | 5.21 | 5.73 | 6.25 | |
| 72 in. | 2.5 | 3.13 | 3.75 | 4.38 | 5 | 5.63 | 6.25 | 6.88 | 7.5 | |
| 96 in. | 3.33 | 4.17 | 5 | 5.83; | 6.67 | 7.5 | 8.33 | 9.17 | 10 | |
| 120 in. | 4.17 | 5.21 | 6.25 | 7.29 | 8.33 | 9.38 | 10.42 | 11.46 | 12.5 | |
| 144 in. | 5 | 6.25 | 7.5 | 8.75 | 10 | 11.25 | 12.5 | 13.75 | 15 | |
| 6/4 | 4 in. | 5 in. | 6 in. | 7 in. | 8 in. | 9 in. | 10 in. | 11 in. | 12 in. | |
| 48 in. | 2 | 2.5 | 3 | 3.5 | 4 | 4.5 | 5 | 5.5 | 6 | |
| 60 in. | 2.5 | 3.13 | 3.75 | 4.38 | 5 | 5.63 | 6.25 | 6.88 | 7.5 | |
| 72 in. | 3 | 3.75 | 4.5 | 5.25 | 6 | 6.75 | 7.5 | 8.25 | 9 | |
| 96 in. | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | |
| 120 in. | 5 | 6.25 | 7.5 | 8.75 | 10 | 11.25 | 12.5 | 13.75 | 15 | |
| 144 in. | 6 | 7.5 | 9 | 10.5 | 12 | 13 | 15 | 16.5 | 18 | |
| 8/4 | 4 in. | 5 in. | 6 in. | 7 in. | 8 in. | 9 in. | 10 in. | 11 in. | 12 in. | |
| 48 in. | 2.67 | 3.33 | 4 | 4.67 | 5.33 | 6 | 6.67 | 7.33 | 8 | |
| 60 in. | 3.33 | 4.17 | 5 | 5.83 | 6.67 | 7.5 | 8.33 | 9.17 | 10 | |
| 72 in. | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | |
| 96 in. | 5.33 | 6.67 | 8 | 9.33 | 10.67 | 12 | 13.33 | 14.67 | 16 | |
| 120 in. | 6.67 | 8.33 | 10 | 11.67 | 13.33 | 15 | 16.67 | 18.33 | 20 | |
| 144 in. | 8 | 10 | 12 | 14 | 16 | 18 | 20 | 22 | 24 |
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