Board feet is a representation of the volume of the wood which takes into account length, width, and thickness. Not to be confused with linear feet which is only length of a board without regard to width or thickness. My rates are primarily based upon board feet with the exception of slabs which I charge in linear feet. In the photo below the 1x12 is the easiest example to understand board feet. One board foot is 1" thick x 12" square. But a board foot is also 2" thick x 6" x 12". The volume of wood is the same in both cases. I charge at the end of the job on finished board feet (not by the hour). I tape and count the lumber we cut to the nearest inch and do the math as follows:

(thickness x width x length x quantity) divided by 144, then multiplied by either .32 or .37

My rates for 2" boards is 32 cents per bdft, and 1" boards is 37 cents per bdft. So if your stack of lumber has 47 2x6's each at 188 inches long, the math looks like this:

(2x6x188x47) divided by 144. The multiplied by .32. $235.62 for 47 boards (+ a bit of overhead for excavator, hired help etc.).