Calculate Board Feet
Volume is the Width times the Length time the Height (or thickness) (W x L x H = Volume)
Lumber is sold in Board Feet, although when you visit the lumber yard, and you buy a 2 x 4, it is still priced in Board Feet.
Here we will provide you with information on how Board Feet is Computed.
Board Feet is a measurement of lumber volume.
A board foot is equal to 144 cubic inches of wood. Actually it's easy to calculate using the following formula:
(Thickness x Width x Length) / 144 = Board Feet
1 inch x 1 ft x 1 ft = 1" x 12" x 12" = 144 cubic inches
Lumber has 2 sizes:
When you purchase a 2" x 4" it is in reality a 1 1/2" x 3 1/2"
Example:
The 2" x 4" is the Nominal Size and 1 1/2" x 3 1/2" is the Actual Size
The following Table is for the Nominal and Actual Lumber Sizes
Note:
Lumber is specified by its rough size (nominal). This is why a 1" x 4" board is (actually) 3/4" thick and a 2" x 4" board is actually 11/2" thick by 3 1/2".
When you are figuring up board feet, keep in mind a waste factor. If you purchase good clear material add about 15% for waste, if you elect to use lower grade material you will have to allow for defects and more wasted material and should add about 30% for waste.
Common Lumber Sizes:
Nominal

Actual

Actual  Metric

1" x 2"

3/4" x 11/2"

19 x 38 mm

1" x 3"

3/4" x 21/2"

19 x 64 mm

1" x 4"

3/4" x 31/2"

19 x 89 mm

1" x 5"

3/4" x 41/2"

19 x 114 mm

1" x 6"

3/4" x 51/2"

19 x 140 mm

1" x 7"

3/4" x 61/4"

19 x 159 mm

1" x 8"

3/4" x 71/4"

19 x 184 mm

1" x 10"

3/4" x 91/4"

19 x 235 mm

1" x 12"

3/4" x 111/4"

19 x 286 mm

11/4" x 4"

1" x 31/2"

25 x 89 mm

11/4" x 6"

1" x 51/2"

25 x 140 mm

11/4" x 8"

1" x 71/4"

25 x 184 mm

11/4" x 10"

1" x 91/4"

25 x 235 mm

11/4" x 12"

1" x 111/4"

25 x 286 mm

11/2" x 4"

11/4" x 31/2" 
32 x 89 mm

11/2" x 6"

11/4" x 51/2"

32 x 140 mm

11/2" x 8"

11/4" x 71/4"

32 x 184 mm

11/2" x 10"

11/4" x 91/4"

32 x 235 mm

11/2" x 12"

11/4" x 111/4"

32 x 286 mm

2" x 4"

11/2" x 31/2"

38 x 89 mm

2" x 6"

11/2" x 51/2"

38 x 140 mm

2" x 8"

11/2" x 71/4"

38 x 184 mm

2" x 10"

11/2" x 91/4"

38 x 235 mm

2" x 12"

11/2" x 111/4"

38 x 286 mm

3" x 6"

21/2" x 51/2"

64 x 140 mm

4" x 4"

31/2" x 31/2"

89 x 89 mm

4" x 6"

31/2" x 51/2"

89 x 140 mm


Example:
2" x 4" (Nominal Size) x 10 feet Long
is Actually 1 1/2" x 3 1/2" x 10 feet
therefore;
1.5" x 3.5" x 120" (10 ft x 12" = 120") =
630 cubic inches / 144 cubic inches =
4.375 Board Feet
where 144 cubic inches is 12" x 12" x 1"
which is 1 Board Foot

