The first step in gelling a liquid is determining how much gelatin to use. The basic ratio of granular gelatin to liquid specified creates a medium-consistency set. If you want to achieve a softer, more delicate set, decrease the gelatin amount. Conversely, if you want a firmer set, increase the gelatin amount.
Additional factors come into play when determining gelatin amount. In making acidic gelatin salads, a higher ratio of gelatin to liquid is needed. The original thickness of the mixture you want to gelatinize is also a factor in determining the amount of gelatin to use. If you are attempting to gel a sauce, such as a velouté or demi-glace, you will need less gelatin because the sauce was already thickened during the sauce-making procedure.