H-1B extension beyond 6years: 1year or 3 years?

Dear all,

I will use up 6 years H-1B by this August, and need to get my H-1B further extended. For the application of my H-1B extension, I wonder if I am allowed to get 1 year or 3 years? FYI Both my NIW 140 and 485 were filed on 09/2005. 140 was approved, while 485 is pending. I am working in a university.

If you know any web/link that provides official info on this, could you please share?

Thank you very much!!