Baggage allowances are pre-decided limit by the particular airline on the capacity of baggage and the number of bags that an individual passenger is authorized to carry. The limits keep on differing from airline to airline, and in sometimes, on the booking fares.
Please Note: Specific weight limit or free baggage exclusion for most of the restricted fares. For the bookings made online, you must check with the baggage-allowance of that particular airline.