How to get the weight of perforated metal sheets

Usually ,most of the perforated sheets we saw are in round holes, with some of patterns ,but the most popular pattern are straight , staggered and 45degrees as following drawing .

weight of finished sheets = original plate weight - weight scraps punched down , the way to get the weight of scraps is to work out the open area firstly , Different pattern , different open area , above drawing showed the most common open area , net weight = Thickness x width x length x (100%-open area) ,for example 1mm x 1m x 2m size , 33% open, net weight is 1mm x 1m x 2m x 7.85 x (100%-33%) = 10.5kg.