Technological advances in wireless networking equipment and atmospheric pressure sensors have enabled the measurement of the pressure distribution across full size sails in normal operation. The pressure measurements may be generated separately on the windward and leeward sides, and on other parts of the rig. Pressure maps of the entire sail can be produced in real-time to provide a detailed time-dependent picture of the pressure distribution, showing the fluctuations and deviations from nominal values due to any changes of the rig, boat motion, or wind. This information is useful in the design process, where sail designers and research aerodynamicists can quantify real-world, full-scale measured differences against computer simulations or alternative sail shapes. It also can be used by sail trimmers to set the best sail shape rapidly and in changing conditions. The pressure sensors are small and lightweight, allowing them to be applied in high density across the entire sail. Laptop software collects and analyses the data, displaying the pressure values and logging the data for post-analysis. This paper provides a description of the technologies used to implement the wireless pressure measurement system, presents examples of the data obtained, and compares the measured results with CFD simulations.