How do you estimate bandwidth usage, in GB/month, for a project that doesn’t have historical data to base numbers on?

Here are some homepage sizes of a few common sites:

Orcsweb.com: 307,487 bytes

Cnn.com: 465,447 bytes

Microsoft.com: 282,788 bytes

Dell.com: 234,655 bytes

Check out the size of your own pages with a free online service like http://www.websiteoptimization.com/services/analyze/

Let’s crank through some numbers real quick. First I’ll use an extreme – take cnn.com since they are the “fattest” site listed. That’s a pretty busy site so let’s say they get 1 million page views a day – just to have a number to work with (probably way low).

So...

Average Page Size in Bytes x Average Daily Page Views = Average Daily Bytes

Average Daily Bytes / 1024 = Average Daily Kilobytes

Average Daily Kilobytes / 1024 = Average Daily Megabytes

Average Daily Megabytes / 1024 = Average Daily Gigabytes

Well, if their homepage was representative of their average site page size, and they got 1 million page views a day, they would consume 13,004GB/month (~13TB) in data transfers.

That of course isn’t representative of average sized sites, so let’s step back and say that a site we are considering has average page sizes of 300kb and the site gets 10,000 day page views (~300,000/month). That works out to around 84GB/month of data transfers.

Note that this is most likely an inflated estimate. Because of client-side caching, compression, and other things, page sizes are often much smaller. For example, at orcsweb.com the homepage is 307,487 bytes but based on our statistics and reporting data, each page view actually sends an average of 35,087 bytes - almost 1/10th of the estimated size.

While these numbers are obviously dependant on the accuracy of the average page size and number of page views, plus other factors like caching and compression, it at least gives a starting point for estimates on bandwidth requirements.

~Brad