There is no easy way to foretell a bandwidth usage. Most search engines, like Google or Yahoo, use robots to visit your website and these robots use different bandwidth compared to human visitors. Website that use database might use different bandwidth compared to website with no database. However, let’s do an easy counting to try to foretell the usage of your bandwidth.

To foretell your bandwidth, you need to build the website first. You then need to be aware of the size of each and every file. (html, image, flash, etc) If you haven’t built your website, the prediction will become inaccurate as you will also need to predict how much disk space is taken by each and every file. If you haven’t built your website it means that you are creating prediction based on prediction, not based on fact.

OK, let’s get dirty.

Let’s assume your main page is an html file with a size of 5Kb. In that page you put 2 images, the header banner is 25Kb and the footer graphic is 10Kb. You also put a flash animation in the middle of the page with 10Kb in size.
That means in total, your main page takes 50Kb. So, what’s next?

That means when a person visits your main page, that person takes 50Kb bandwidths. Most browsers will have a cache feature turned on. When the person visits your site, the browser downloads the contents, all 50Kb of them, to the person hard drive. If the person refreshes the browser, more often than not, the content will be taken from the cache. This means that person does not take any bandwidth for this action. Nevertheless, if the cache session is over and the person refreshes the browser, that person is taking another 50Kb bandwidths from you. Thus, from that one person, you need to prepare 100Kb. If tomorrow this same person visits your website again, most likely the cache session is over and that person will take another 50Kb bandwidths from you.

Simply put, if you are expecting 250 people visit and refresh your main page in a day, you need to prepare: 250 people x 30 days x 50Kb = 375,000Kb or 375Mb bandwidth. Notice that the counting above only includes one webpage of your website. If you expect each visitor to visits 5 web pages of your website, you need to prepare: 375Mb x 5 web pages = 1,875Mb or 1.875 GB, which is almost 2 GB bandwidth. Also, that bandwidth counting is only from human visitors, you also need to put search engines robots into consideration. You could perhaps expect one robot to visit your page once a month or once a month or even once a day if your website is that good. That means the 1.875 GB could roughly be rounded to 2 GB while taking search engine robots into consideration.

You also need to pay attention that the example above is only assuming that you will have 250 visitors a day or 7,500 visitors a month. In general, for a website to be counted as a working website, most people will agree that 100,000 visitors a month is the minimum. With that number, you need to plan: 100,000 visitors x 50Kb x 5 pages = 25,000,000 Kb or 25 GB bandwidths each month. If your website is an advanced website with lots of graphics and flash animations to make the website more beautiful, you need 200Kb for each webpage. Thus making the bandwidth 4 times bigger or 100 GB bandwidths needed each and every month. If you are successful, you could have 500,000 visitors or more each month and that will make the number even bigger.

In summary, the bandwidth you need to run your website successfully could be foretold beforehand. Several main factors you need to take into consideration while counting bandwidth are: number of visitors each month, the total size of your pages, and how many pages you have on your website. You also need to prepare additional bandwidth for search engines robots visit and several additional bandwidths that are taken when you use database such as MySQL