if you belong to general category then it is less likely that you would get seat on basis of your jee mains marks. You essentially need to clear advanced also. In case of reserved category you will surely get a seat in nit if you are able to clear jee mains examination

For sc and st it is ( percentile ) between 80 to 90

In case of obc it ( percentile) is around 92 to 93

Further if you wish to choose top nits with stream of your choice you need to get anything around 95 or 96.

In case of general category it is very less likely to get nit only through jee mains, if it happens you need to get a percentile of around 98 or 99 and wait during counselling.