Evaluating and understanding the complex array of factors that influence consumer decision-making in the realm of sustainable practices will play a crucial role in fostering a more eco-conscious society. The study developed the Green Consumer Behaviour Index (GCBI) as a tool to provide regular quantitative measures of consumer behaviour and to promote sustainable consumption by increasing consumer awareness, providing individual reference points for comparing their own consumption patterns. The GCBI was formulated considering food and water consumption, purchasing behaviour, energy and transport, and household waste management with five individual performance evaluation levels. A semi-structured questionnaire was used to evaluate the 131 participants’ (between 16 and 70 years old) GCBI index following the purposive sampling technique. According to the evaluation results, 42.5% of participants’ GCBI value was recorded under the unsatisfied category due to their fewer green practices on those evaluated categories, while 8% of the participants showed outstanding scale performance. For the other three levels in GCBI, very satisfied, satisfied, and poor levels represented by 16%, 20.5% and 13% of the total participants respectively. The developed index and the research findings will assist consumers, producers, policymakers, and academics in promoting sustainable consumption, reducing environmental impact, and creating opportunities for businesses and policymakers to develop effective strategies.