You would need to know the pressure of the gas to answer that. Does the container specify the pressure of its contents? The gas law requires that you know the volume and pressure of the gas. 12 grams specifies its weight. And without looking up the specific cartridge, I don’t know if that’s the gross weight or weight of the empty container. If you can find both weights, you can also subtract and find the actual weight of gas, which would get you to its volume at a given pressure, say 1 atmosphere.