it depends upon the school you are trying to get into.  i have seen people who came here 3 years degree from nepal and took another three years to complete their undergrad from US institution.  also, i have seen at least one who completed in one year.  so, you can assume you can transfter minimum of 30 credits to maximum of 90 credits i guess .  i am not sure though.  it also depends upon your grades back home.  it is good idea to evaluate your transcript while applying to colleges here if you are already in usa.  www.wes.org is one of those organizations who will evalutate your 3 years program on course by course basis.  hope this helps.