I mix mine by volume. I make 200ml at a time in a 250ml plastic bottle (I leave the extra room to allow a good shake once all the ingredients are added), then break that down into two 100ml squeeze bottles. I use glass graduated cylinders in 10ml and 100ml size to measure everything out. I only do unflavored, so I only have to worry about nic base, vg, pg, and distilled water.