There are hundreds of sites that offer conversions from linear foot measurements to board foot measurements and visa versa. In Crate Pro > Inventory > Lumber the 1 to 1 calculation is already there:  For each lumber material in Level A which is Linear Foot measurements, the next column is the value for Board Foot based on one Linear Foot. It can be a % or a whole number. If you know the number of linear foot you have, simply multiply it by the BF value to get the total number of board feet. If determining your cost: divide the cost you paid by the total board foot purchased.

Imperial dims for lumber have an 'actual' value and a 'nominal' value. Actual are the dimensions Crate Pro 6 uses for determining dimensions. Nominal values determine board footage. 

Setting your Tracking Level by Board Foot in Crate Pro, usually done for ISMP15 tracking purposes and is one of the most common ways of purchasing lumber. However, you may purchase your material by the piece or by linear foot. Do NOT change your Tracking Level once set, just convert the values. 

The following is provided by: Hardwood  If you want to be geek smart...

There are also many sites that have handy calculators that you just enter the information: Such as Amerhart Lumber Footage Calculator. Easy to use. Always enter Nominal dimensions and not Actual.

 Once you have the total board footage of your purchase you just take the dollar amount paid and divide the total purchased board footage.