Antonio Gulli, who I've mentioned before at SEOmoz, has an online report on the size of the world wide web. It's a detailed description of the process and results of his inquiries into the indexable portion of the web, which he currently estimates at about 11.5 billion pages (plus this new one I've just created).

The study also details the coverage of the indexable web by the current top commercial search engines:

• Google=76.16%
• Msn Beta=61.90%
• Ask/Teoma=57.62%
• Yahoo!=69.32% 

This can be useful if you'd like to know how many links Google, Yahoo!, MSN or Ask may be aware of. Since Yahoo!'s Linkdomain command gives the most reliable estimates as of today, a little math can help you have a good estimate of the number of links MSN, Ask & Google know about.

If you have 100 links according to Yahoo!, here's the formulas:

• Total Links on WWW = 100 * 1.44285
• Google = 144.285 * 0.7616
• MSN = 144.285 * 0.619
• Ask/Teoma = 144.285 * 0.5762