So you now show total inches on your BOM with this method correct? The only downfall is it doesn't take into consideration yeild on the 12' stock length. IF your assembly calls for 4 nine foot pieces you will end up with 4 three foot pieces left over and your inventory will show 12' of material in stock when in fact you have 4 three foot cut off pieces in stock. This is the part our company is struggling with in respect to keeping accurate inventory and purchasing correctly.
ERP, and material stock lenghts and offcuts have always been a pain. From memory SAP Business One had a very handy materials length system that catered for offcuts being returned to stock and for length nesting. We don';t use it (or any other). Still have not found the best for our needs.
I guess I am not sure I am thinking the same as you, maybe your material you can splice together? I am unsure what material you are working with.
In my mind, if you had parts that were say 7 feet long (you said your stock size is 12 feet) and the assembly called for 12 of these 7 foot long pieces, that would equal 84 feet total. So how does your purchasing software tell you "hey total feet is 84 but you still need to order 12 pieces because you can only get one 7 foot section out of each 12 foot piece"?