Go to yahoo or Google and type this site:http://www.packersmoversin.com. In Google it will show all the pages of a site and in Yahoo it will also show the number of pages but it can also show the number of backlinks of a site.
Why do you not know!?! Surely as a webmaster you should have an idea at least. For a site using a CMS this is an easy job. Like all of the posters above have said - you're going to have to count them, or let a sitemap tool count them for you. Theres no other way. You dont have to submit it to Google to count the pages, however I'd reccomend you do submit it regrdless so that Google can start to find you!
Your script should have this basic feature if you are using php cms of some kind. If standard html then that might be a different story, but still fairly easy to figure.
As stated before, this will only tell you the number of pages that are indexed by Google, not how many pages exist on the site. Google may not index every single page on your site. in fact, it's very unlikely that this will happen unless all of your content is super relevant for your niche. External tools, counting the pages, or by using CMS functions seem to be the answer.
Have a constantly updating sitemap using cron jobs and using php scripts which reload and act again and again in order to make sure the number of pages you have are indexed properly into a sitemap AND that sitemap is submitted to the search engines consistently
Tried it, works good! Thanks, I can recommend it to all of you! I tried other programs earlier but none of them give me the real number, this is a reliable one!