A seasoned stoner will be able to give you a rough estimate as to how much weed there is in a baggie of any given size. The reason being that you quickly get used to knowing what a decent eighth of ounce looks like. However, a true pothead of superior proportions will usually have the ability to weigh weed by sight with the most ridiculous level of accuracy. They’ll identify the strain, consider the specifics of the plant matter and tell you within a fraction of a gram how much you’re looking at. Which is a skill developed for one reason and one reason only – to prevent getting ripped off. Actually that’s not quite true – it also makes a great party trick, not to mention a great way of wagering whatever you want and knowing you’ll win.