Purpose: Employing a theoretical model of human behaviour (COM-B), the current study explores the factors influencing farmers' engagement with grass measurement on Irish dairy farms. Methodology: The current study employed a qualitative research design. One-to-one semi-structured interviews were carried out with 21 dairy farmers. Findings: Factors inhibiting farmers from engaging in grass measurement included a high perceived task effort, a lack of skill and self-efficacy to carry out the task, uncertainty over personal value of engagement, a lack of tangible support, and a confidence in, and preference for, existing intuition-based decision-making. Practical implications: Recommendations for communication, extension, education and technology development are offered to tackle the 'high task effort' associated with grass measurement by farmers and to support skill development and self-efficacy of dairy farmers. Theoretical implications: The study proves value in moving from behavioural frameworks which focus solely on individual constructs as 'barriers to adoption' towards using frameworks which also account for the important role of factors external to the individual such as their social and physical surroundings. Value: A comprehensive theoretical framework is offered for understanding dairy farmers' engagement with grass measurement along with evidence-based suggestions for communication, extension, education and technology development.