What is bandwidth 
The terms bandwidth and data transfer are often used interchangeably by web hosting companies. Although closely related, the two terms do in fact mean different things. Bandwidth is the amount of data that can potentially be transferred at one time, whereas data transfer is how much data is actually being transferred. However, as I said, you’ll find a lot of web hosting companies using the term bandwidth as a measure of how much data you can transfer per month. The various plans offered by web hosting companies will include some measure of the amount of bandwidth that your site will be able to use. This figure is normally given in gigabytes (Gb) per month, for example a plan may offer 5Gb/month. This means that the total amount of data transfer used by your site for any purpose should not exceed 5 GB. So, how much bandwidth will you need? If you already have a site up and running this should be fairly easy to estimate, based on the reports available from your current web host. If this is a new site then you will need to make some estimates. You will need to know the number of visitors you expect per day, the number of pages you expect each visitor to look at and the average page size. Then multiply all three together, to give you a daily total. Then multiply that figure by 30 to get a monthly total. You will also need to allow for email usage, and for any uploads needed to update and maintain the site. If you plan to offer file downloads then you will need to factor that in too. Remember that the figure you calculated is the bare minimum needed to keep your site running, and it is only an estimate. You will need to add in a margin for error, and also an allowance for future growth – as your website becomes more popular then your bandwidth usage will increase.
