A SIMPLE model to estimate the optimum irrigation water consumption (OIC) of sugarcane and annual crops was developed. The FIVE-CoRe (Farm Irrigation Volume Estimation according to Constraints and Requirements) tool was designed for use at individual farm and irrigated scheme levels. It functions on a daily time step and takes the main physical factors that determine water requirements, irrigation strategy, and some technical constraints associated with this irrigation into account. It was implemented for 3 years in southern Réunion to assess OICs of sugarcane in a cropping area of around 2500 ha (22 micro-areas). The mean cumulated OICs simulated by the model were generally close to the actual irrigation water consumption (AIC) levels. This showed that the model can efficiently estimate AICs despite its simple conceptual design and the 1- to 3-fold variability in annual accumulated irrigation for the micro-zones. In two micro-zones, however, there were marked differences between AIC and OIC values. FIVE-CoRe can be used to test irrigation water volumes under different irrigation scenarios and strategies. Gaps between AICs and OICs were indicators of the efficiency of irrigation practices. FIVE-CoRe could also be used to simulate irrigation water volumes for crops under different climatic scenarios, irrigation strategies and for sensitivity analysis.