So, the answer differs according to the various reservation categories and it also changes depending on the year of the exam. So, what I am writing here is merely a general estimate.
For the general category, you’d need to have an All-India Rank (AIR) that does not go beyond the range of 75-95 if you want to be an IAS officer. For OBC, the rank cannot be greater than the range of 460-470, For SC, 840-650, and for STs, 765-775.