Delivering popular web pages to the clients results in high bandwidth and high load on the web servers. A method to overcome this problem is to sendth ese pages, requested by many users, via multicast. In this paper, we provide an analytic criterion to determine which pages to multicast, andan alyze the overall saving factor as compared with a unicast delivery. The analysis is based on the well known observation that page popularity follows a Zipf-like distribution. Interestingly, we can obtain closed-form analytical expressions for the saving factor, that show the multicast advantage as a function of the site hit-rate, the allowed latency andthe Zipf parameter.