Inclusive checked baggage allowances on British Airways
General rules
As a rule of thumb, you should refer to the baggage policy published by the operating carrier and this generally applies when flying on a codeshare flight. Well, almost. While in most jurisdictions where the policy of the operating carrier applies to your individual baggage allowance, things are done a little differently in the United States where the policy of the marketing carrier governs. Something to be mindful of when travelling on BA/AA joint venture services.
When travelling with British Airways, the maximum baggage size accepted at check-in including handle, wheels and other protrusions is currently 90cm x 75cm x 43cm (35.5in x 29.5in x 16in). The allowance and maximum weight per bag is dependent on the class of travel and status, as illustrated by the slides below.
When a party includes a Gold card holder an additional checked bag applies to all passengers travelling on the same booking. However, the higher weight of 32kg per bag applies only to baggage belonging to the Gold card holder, so the rest of the party will have to ensure the weight of their bags does not exceed 23kg.
Like Gold card holders, the allowance for Silver card holders also includes one additional checked bag when travelling on BA flights.
Travelling in more than one cabin
If you are travelling in more than one cabin, e.g. outbound in economy and return in business class, you will be given the more generous allowance for the whole journey.
Basic fares
If you purchased a Basic (Hand Baggage Only) fare (available in Euro Traveller) and later decide to check bags in, this is still possible upon payment of a nominal fee. Paying this charge is cheaper when done online than it is at the airport.
Note, Infants and children travelling on a Basic fare may still check a fully collapsible pushchair (stroller) and a car seat free of charge.
Inclusive allowances
Travel to/from Brazil, Ghana, Kenya, Kuwait, India, Japan, and Pakistan
and
Connecting journeys between India and USA/Bermuda/Canada
and
Connecting journeys between Saudi Arabia and USA/Bermuda/Canada

See:
Recent changes to baggage allowances on flights to and from Brazil
Additional allowances for infants and children
These additional allowances apply to all cabins, including Basic (Hand Baggage Only) fares.