Measuring the Web with Lycos

Michael L. Mauldin, Carnegie Mellon University, Pittsburgh, PA, USA or or
Web Size, Information Discovery and Retrieval

What is the Web?

The first question to answer in measuring the size of the web is to determine what counts as being ``on'' the web. We define the web as any document in either By design, Lycos does not index ephemeral or changing data or infinite virtual spaces. Therefore, the following are not considered part the web: Further, we do not consider the output of CGI scripts as part of our count. To codify this constraint, we ignore URLs containing either a question mark (?) or an equals-sign (=), as these characters are of primary usage for CGI scripts. We also eliminate some URLs such as the human genome database or the Blackbox glossary, which encodes user state information in the URL (without this limitation, a robot could count a single page with state information an infinite number of times).

The figure shows our taxonomy of CyberSpace, showing that Lycos' view of the Web is a strict subset of the Internet, but is larger than simply the space provided by HTTP servers.

Sampling the space

Lycos samples the web continuously, and the search results are merged with the catalog weekly. To estimate the size of the web, we take a week's worth of new searches, assume they are an independent random sample of the web as a whole, and multiply the old document size by the ratio of the size of the new sample set to the size of the intersection of the two sets.

As of April 4th, 1995, the ``old'' document set contained 2,687,146 known URLs. The new search consisted of 680,011 URLs, of which 408,839 were also in the old set. That gives a ratio of 1.508, multiplied by the old size gives 4.051 million URLs.

Other Measures

How many servers?

Between Nov 21, 1994 and April 4, 1995, Lycos successfully downloaded at least one file from 23,550 unique HTTP servers.

What is the distribution of file types?

	        Cataloged	  Downloaded

ftp            486906 (16.5%)	  31931 ( 6.2%)
gopher         736091 (24.9%)	 106340 (20.6%)
http          1722152 (58.2%)	 377505 (73.2%)
mailto            276 		   NA
news              218		   NA
rlogin            157		   NA
telnet          11401 ( 0.4%)	   NA
wais              784		   NA

total	      2957985		 515776

How big is the average document?

During that same time period, the average text file size downloaded was 7,920 characters.

So how big is it?

Multiplying gives an estimate of 32 billion bytes (29.9 gigabytes) for the size of the web.

Sources of Error

The biggest problem with this number is that the search is almost certainly not a truly random sample. Lycos uses a biased weighting scheme to download ``popular'' documents first, so the new search will tend to overlap the old more than a truly random sample.

Since the size of the intersection is therefore inflated, and since it's in the denominator, the estimate of 4.051 million is a lower bound.


Lycos is generously supported by funds from Carnegie Mellon University. Some of the hardware is re-used from the Tipster Data Extraction Project funded by ARPA. Dr. Mauldin is also funded by a research grant from the Corporation for National Research Initiatives as part of ARPA's Computer Science Technical Report project.

Lycos is a registered trademark of Carnegie Mellon University.

Presented at the Third International World-Wide Web Conference, April 11, 1995.
Last updated 7-Apr-95