If you have absolutely no idea, and want a good result, then it can't be done.
If its a jug, of very concentrated acid, that somehow -- on the label, in the MSDS, your boss's opinion, popular knowledge about your lab -- gives you some idea of the concentration, then you can work with that, with varying possibilities of success. In ancient times, works like concentrated, dilute, strong, weak actually stood for certain concentrations, that depended on the acid or base. Most people have stopped doing it that way.
Or you analyze the concentration, or buy a new bottle of the known concentration.