Carbon nanotubes show great promise as a new class of electronic materials owing to the change in their electrical properties with chirality of the nanotube. On one hand, they can rival the best metal and on the other, a semiconducting nanotube can work as a channel in a nano field effect transistors. The energy band structure and density of states of SWNTs of different chiralities is reviewed here and using a diameter dependent model, the electrical conductance of a single wall nanotube (SWNT) and a multi wall nanotube (MWNT) is analyzed. It is found that conductance of a CNT depends largely on its geometry and an MWNT shows very high conductance which varies with average tube diameter, length and number of shells in the tube. This study would play an important role in understanding the working of various CNT based electronic devices.