Aims: To develop a theoretically and psychometrically sound instrument to measure the ‘dose’ of person‐centred care practice in long‐term care. Background: Although person‐centred care has been adopted for long‐term care across the world, there is a lack of theory‐based instruments to measure its impact. Two questionnaires were developed to measure person‐centred care from the perspectives of staff and family based on current person‐centred care frameworks: Kitwood, Nolan, and Eden Alternative. Methods: Phase I: literature review and focus groups identified potential items for the questionnaires. Phase II: academic experts, local staff, and family members of residents assessed content validity. Phase III: psychometric testing. Results: A 34‐item staff questionnaire (Cronbach’s Alpha = 0.942) with two factors “Making person‐centredness real” and “Making the environment meaningful for life and work”. A 30‐item family questionnaire (Cronbach’s Alpha = 0.947), with three factors “Staff care about what is meaningful to my family member”, “Staff know and respect my family member”, and “We are all part of a family”. The factors did not directly reflect the theoretical constructs from Kitwood’s and Nolan’s work. Conclusion: Two instruments, capturing the ‘dose’ or active practice of delivering person‐centred care, have demonstrated sound psychometric properties. The study contributes to understanding the theoretical components of person‐centred care. Impact: The study addressed the lack of robust tools to measure how much person‐centred care is taking place in aged care facilities. Staff and family questionnaires were produced based on strong theoretical foundations combining concepts of prominent person‐centred theories and rigorous psychometric testing. The instruments can be used to determine if person‐centred care makes a difference, to compare if person‐centred care changes or develops over time or between facilities. Ultimately residents, families, and staff will benefit from the ability to measure how much person‐centred care residents receive.