With increasing political pressure to produce more food whilst being environmentally and socially considerate, alongside the need to cope with climatic extremes and financial instability, farming needs to become more sustainable. To monitor and improve understanding of sustainable agriculture, farmers will need additional tools to illustrate the impacts of their business decisions. However, current tools to monitor the sustainability of agriculture require measurement of variables that are rarely readily available. Moreover these tools exclude farmers in their development and interpretation. This paper suggests a pragmatic approach to creating a farm-based monitoring tool. We propose that farm-level indices of sustainability are initially based only on data that is readily available. Whilst this would increase its appeal to farmers and therefore participation rates, it may initially have little immediate value as a measure of sustainability. Therefore a ‘design-action-design’ cycle-the basis of adaptive co-management- must be employed to allow the tool to evolve. Starting from this pragmatic, bottom-up perspective, as data collection systems improve, more theoretically driven (i.e. top-down) site-specific variables of sustainability can be included to provide a more comprehensive tool. This paper illustrates the principles involved by (i) calculating a farm-specific composite sustainability index (CSI) for a commercial farm based on readily available data and (ii) emphasising the need to establish better data collection systems.