Depending upon how deep of a hole you want to put into the glass, the 80 grit could be as little as a 1/2lb. but 1lb is a better thing to get. The rest, a 1/4lb. is usually quite sufficient, especially in the smaller grits where an oz. is often enough. The secret to having plenty left over is to not let most of the grit slosh over the tool and fall on the workbench when grinding. I've seen people run out of grit at every stage of grinding with a kit and yet others have almost all of the grit that they were given. It's not to say that one poured too much grit on but rather he put so much water on that he washed the grit he did put on rather than use it for grinding the mirror.