What bar spacing do I need for my bird?

It depends on the species. Across specialist communities, the consensus is that finches and budgies need narrow spacing (roughly 3/8 to 1/2 inch) to prevent escapes and head entrapment, while cockatiels and small parrots do well around 1/2 to 5/8 inch, and larger parrots like African Greys need closer to 1 inch with thicker-gauge bars. Reviewers in r/parrots repeatedly warn that a cage with wide spacing but a small footprint is the worst of both worlds.