There are two ways: the first actual quantity of material\/quantity of material used (for example, the actual material used in a batch of processing 10000, the number of throwing materials 100, and the throwing rate 1%)
The second: [(actual number of materials issued - theoretical number of materials) - actual number of remaining materials)]\/ (actual number of materials issued - actual number of remaining materials) This way is easier to operate in reality. For example, a batch of PCBA patches, the material is the same 0805 1w light-emitting diode, 1pcs board paste 10, to paste 1000pcs. The warehouse sent the whole plate of materials 4000*3 =12000, the theoretical number of materials 10,000, the actual number of returned surplus materials 1800. Throw rate (112,000-10,000-1800)\/(112,000-1800)=1.78%.
I hope it will hlep.