Like perhaps a 9mm Luger case level full would equal 'X' number of grains volume???
About 13 grains of black powder based on the case having a capacity of 13.3 grains of water. Water and black powder happen to have nearly identical densities so if you know the case capacity in H2O, that's about the amount of black powder it will throw if used as a powder measure.
You can find charts of case capacities in H2O with an internet search.
.357 Magnum measures about 27 grains.
.30-30 measures about 45 grains.