I have exchanged my forum to about 15 forums, their are pr 3,4,3,4,2,3,4 Only one site is 0and 1. Do you think how pr I will get?
Who knows? I wouldn't really be concerned about the PR of your site in terms of getting a top ranking in the SERPs. Just keep building "quality" backlinks to your site..
First of all, no one will be able ot calculate it. There are a few pagerank prediction tools around, but none of htem are really very accurate. You need to keep in mind that there are many factor involved in determining your pagerank. Including, the pr of the actual page your link is on, the number of outbound link on the page your link is on, whether or not your link is no follow, and many, many more.