A turbulent jet breakup model is derived using concepts from probability theory. Velocity fluctuations at the free surface are hypothesized to be the cause of turbulent jet breakup. This idea is formalized by treating the fluctuations as random variables, subject to damping from the free surface. In contrast to previous theories, this theory uses a conditional ensemble average to determine quantities of interest because not all fluctuations produce droplets. An energy balance and a closure model are used to determine the Sauter mean diameter. Similar approaches are used to determine the breakup onset location, breakup length, and spray angle. To validate the model, data from previous experimental studies using long pipe nozzles was compiled. Data for rough pipes was used to include turbulence intensity in the study.