Assessing the size of the Internet is a somewhat difficult proposition, since it is a distributed body, and no complete index of it exists. What we mean by asking how large the Internet is also plays into how we answer the question. Do we mean how many people use the Internet? How many websites are on the Internet? How many bytes of data are contained on the Internet? How many distinct servers operate on the Internet? How much traffic runs through the Internet per second? All of these different metrics could conceivably be used to address the sheer size of the Internet, but all are very different.
Perhaps the simplest metric is simply how many people use the Internet. This can be viewed as the population of the Internet, and so would seem to be a decent gauge of its size. Many different companies try to measure Internet usage, ranging from Nielsen Ratings to the Office of the CIA to Serverwatch. The general answer seems to be that just over a billion people used the Internet in 2008. Of these, about 500 million use the Internet at least once a week, making them more-or-less permanent citizens of the Internet population.
It may be that what most people mean when they ask the size of the Internet is how many bytes it takes up. Estimating that is a fairly difficult task, but one person made an estimate not so long ago who can probably be trusted to have a good idea. Eric Schmidt, the CEO of Google, the world’s largest index of the Internet, estimated the size at roughly 5 million terabytes of data. That’s over 5 billion gigabytes of data, or 5 trillion megabytes. Schmidt further noted that in its seven years of operations, Google has indexed roughly 200 terabytes of that, or .004% of the total size.
There are thought to be some 155 million websites on the Internet, but this number fluctuates wildly from month to month, and one runs into a problem of what exactly constitutes a website. Is a person’s individual Facebook page its own website? How about their LiveJournal or blog? What if the blog is hosted by a blog service?
Other metrics for the Internet's size run into problems with finding any reasonable numbers on them. People estimate there are roughly 75 million servers worldwide, but this number may be off by up to a factor of five. The traffic that runs through the Internet in a single day might seem like it would be easily measured, but in fact it is very hard to find a reliable collection of this data, because of the sheer amount of computers, servers, and nations involved.
Perhaps the best way to conceive of something as inconceivable as the size of the Internet is to follow the lead of Russel Seitz. He took estimates for size and traffic of the entire Internet, and used this with the weight of the energy used to move a byte of information around. Although minuscule individually, over trillions and trillions of bytes it slowly added up. How large is the Internet? According to Russel Seitz: two ounces.