In theory, you could use 30 mg of tissue per antibody per ChIP. You will start by optimizing conditions for the type of tissue you work with. The exact amount of tissue to start with depends on the relative abundance of the protein of interest in the tissue, on how good the antibody is (ChIP grade, ...) and also on how efficient the crosslinking is, ... and so on. In another words, conditions must be optimized with each sample and conditions.
