You do not need to estimate; simply buy a connecting ticket and it is the airline, rather than you, that needs to worry about such things.

If, instead, you are piecing together your own "connection" by booking separate journeys on separate tickets, you should be maximising the time at your connection point so that any delays (whether in the flight itself, or the delivery of checked-in luggage from that flight) do not spoil your plans. When travelling on separate tickets, if you miss your connection, you will have to pay for a replacement ticket at the last-minute walk-up fares.