It really depends on what you are trying to sink. It does not take much to sink open PVC pipe but will take a lots for sinking a bamboo condo. Some woods are heavy and will take less weight than other type woods that are less dense that will take more weight. I learned my lessen years ago when I tried to sink a bamboo condo with a half bucket of Quick rete. It floated and I had to pick it up and take it back home and fill it full then bring it back the next day to sink it. Better to have to much weight than too little is now my thinking.