The basic calculation of board feet (aka B') is width (in inches)
multiplied by height (in inches) multiplied by length (in feet)
divided by 12.
(W x H x L)/12
So to give you an idea, one way of imagining one board foot is
a 12 inch square piece of wood that is one inch thick.
{Just to complicate things a bit, the thickness of rough wood
or lumber is measured in quaters. One inch = 4 quaters, written
out like this: 4/4. Two inches = 8/4.}
* Put new values into the form, and it will keep a running total.