Designing crop ideotypes in silico is a powerful tool to explore the crop yield potential and yield gap. We defined yield gap as the difference between yield potential of a crop ideotype optimized under local environment and yield of an existing cultivar under optimal management. Wheat ideotypes were designed for the current climate using the Sirius model for both water-limited and irrigated conditions in two high wheat-productive countries viz. the United Kingdom (UK) and New Zealand (NZ) with the objective of estimating yield gap. The mean ideotype yields of 15.0-19.0 t ha-1 were achieved in water-limited conditions in the UK and NZ, whereas 15.6-19.5 t ha-1 under irrigated conditions. Substantial yield gaps were found in both water-limited, 28-31% (4-6 t ha-1), and irrigated conditions, 30-32% (5-6 t ha-1) in the UK and NZ. Both yield potential (25-27%) and yield gap (32-38%) were greater in NZ than the UK. Ideotype design is generic and could apply globally for estimating yield gap. Despite wheat breeding efforts, the considerable yield gap still potentially exists in high productive countries such as the UK and NZ. To accelerate breeding, wheat ideotypes can provide the key traits for wheat improvement and closing the yield gap.