272g / 12 g = 22 2/3 units....
12g CO2 cartridges are usually around $1/each...
At $23 per 1/2bbl dispensed in CO2 cost alone, this could possible the least economical way to push beer out of a keg!
A proper 5lb CO2 tank setup will cost you MUCH less in the long run.

Another thing to note here is that it is very difficult to maintain the proper level of pressure with these little cartridges, they are intended for special event (1 day only) and remote use.