For fly lines 8wt and above use 30# cores, lines from 2wt through 7wt use 20# cores generaly. As leaders and tippet go a general rule of thumb is to take the x indication and subtract it from 9, so a 5X tippet would be 4 pound test roughly.
The only way to tell for sure about the tippet would be to look on the website of the company that made it. One company's 0X could be 8lb while another's is 15lb.