Rejections in bill ofmaterial

Lets say I wish to compute BOM quantity to produce 1 KG of Cloth. Here I need to know how much Yarn I need to produce 1 KG of cloth. Now, I will consider the process loss that will occur during processing and decide that I will have 200 gms of wastage. Now My BOM quantity should be 1.2 KG. Here I got suggestions from others to add my rejections like 2% of raw material required. Is it correct?