Hello Aspirant,

No this is not valid estimation because it is not necessary that if the total number of seats are 16,000 then the candidate securing rank 16,000 will get admission for sure, the reason being is that there are some rank positions on which more than one candidate get placed. Suppose that you have 16,000 rank and there are 10 students on 20th rank so here your estimation will become wrong.

To know your chances in different IITs you can check out previous year's JEE-Advanced cut-off for IITs from  the link given below :-

https://engineering.careers360.com/articles/jee-advanced-cutoff-for-iits

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

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

I hope this information helps you.

Good Luck!!