What is the size of the Web? The estimates vary from 15 to some 30 billion Web pages.

One of Pandia’s most popular articles ever is On the number of Web sites in the world from 2000. This proves that many of us find the tremendous growth of the Web both fascinating and — maybe — a bit intimidating.

In 2000 the size of the Web was reckoned to be some 7 million unique sites, a 50 percent increase compared to 1999.

A 2005 study estimated the World Wide Web to contain 11.5 billion pages (not sites) by January 2005.

In 2005 Yahoo! announced that its search engine index contained more than 19.2 billion documents. Given that Yahoo! does not cover all documents on the Web, it is reasonable to expect that the real number is higher.

However, keep in mind that the term “documents” will refer to more than web pages. On the other hand, the Yahoo! figure will also cover duplicate content (several versions of the same page, given different URLs etc.) and a lot of spam.

The ISC Internet Domain Survey is trying to count the number of hosts on the Internet. The figure for January 2007 was 433,193,199. A host is identified by its domain-name (for instance: pandia.com).

However, Netcraft presented a totally different number in late 2006, saying that there was at the time around 100 million web sites with domain names, out of which 47 to 48 million were active sites.

The February 2007 figure from Netcraft is 109,000,000. The difference between the ISC and Netcraft number may be caused methodological differences and the fact that the two companies are not able to identiy all domains.

Note that the number of hosts is not equal to the number of Web sites. There may be many Web sites under one host. Google’s Blogger blog service will for instance host a large number of blogs under its blogspot.com domain.

Based on Netcraft’s data Boutell estimates some 29.7 billion pages on the Web in February 2007. However, the methodology underpinning this number is very weak, to say the least.

All this leads us to conclude that the number of web pages must be somewhere between 15 and 30 billion — and probably closer to the latter than the former, given the increase in the number of Web users, bloggers and companies moving online since 2000.

Note also that Internet World Stats counted over 1 billion Internet users in 2007.