A small helium tank measures about two feet high. Yet it can fill over 50 balloons! How can such a small tank contain enough helium to fill so many balloons?

It will only take a small amount of helium when inflating balloons. For example, an 11" balloon only needs 0.015 m3 of helium. So it make sense, why a two feet helium tank can inflate at about 50 balloons. Also, the size tank (2 ft. high) does not define the capacity of helium it contains.