Hi,

Actually there is no exact formula through which you can calculate category rank from CRL rank because it may differ depending upon numerous factors like number of total candidates, total candidates from the OBC category and so on. But if we go through the analysis of CRL Vs OBC ranking for JEE-Main 2020 then according to the CRL rank mentioned by you in the question your OBC rank is expected to be in the range of  13000-14000, you can also check out marks Vs ranks Vs Percentile from the link given below :-

https://engineering.careers360.com/articles/jee-main-marks-vs-percentile

Or

You can also use JEE-Main Rank Predictor to predict your rank :-

To have a list of all those colleges which you can get based upon your marks, category, and state you can use JEE-Main College Predictor:-

https://engineering.careers360.com/jee-main-college-predictor?icn=QnA&ici=qna_answer

Hope this helps!