Culture fit is often judged by gut feel at the end of an interview, which is where problems start. A clearer version breaks it into specific, observable behaviours, such as how someone handles feedback, works to deadlines or shares information with colleagues. Interviewers can then ask every candidate the same questions about those behaviours and rate the answers against agreed examples.
Left undefined, culture fit easily becomes a proxy for similarity: shared hobbies, accent, schooling or sense of humour. That can narrow the workforce and expose an employer to discrimination complaints. Good practice is to write down the values that genuinely affect performance in the role, test them with structured questions and challenge any 'not a fit' comment that cannot point to evidence.