Bandwidth
Bandwidth (data transfer) is usually measured in gigabytes. A gigabyte is roughly one billion bytes. Each letter on this page is one byte. Images can take up a large amount of kilobytes (thousands of bytes), and file downloads can be several megabytes (millions of bytes) in size.
Unless your site has a lot of downloads or a large advertising push, it will be unlikely that you will need many gigabytes of transfer - 2-5 gigabytes should be enough. Any more, and you will just be paying extra for something you will not use. On that note though, you should be careful and make sure you always do have some extra bandwidth.
As part of our commitment to quality, we consistently monitor performance and data transfer rates of all the websites on our hosting servers. All our hosting accounts are upgradeable and extra bandwidth can be assigned if needed. The fee for extra bandwidth is $5 per gigabyte per month.