Idea: Each individual copper layer is assumed to provide the very same finished copper fat Except if usually specified in your fabrication notes. A 4-layer board with a defined excess weight of 1oz, is assumed to have a concluded copper thickness of 1.37mils (or even more) on each copper layer. https://16-layer3-levelhdipcb73715.izrablog.com/31779209/examine-this-report-on-8-layer-first-order-pcb