Intrinsic stress generation during film deposition can lead to failure by processes such as cracking, delamination and peeling. Crystallite coalescence is a suggested mechanism for intrinsic tensile stress generation during film growth and various analytical models have been proposed to describe this phenomenon. In the past, researchers have not been able to measure this stress precisely because the stochastic nucleation of islands results in coalescence over a range of different times and length scales. We use a technique to control the island geometry using selective growth of films on patterned substrates. Ni films were electrodeposited on patterned Si (001) substrates using the above procedure, and in situ stress measurements were then used to study the tensile coalescence stress as a function of growth rate and island size. In these studies, most of the incremental tensile stress occurs after the initial contact of neighboring islands and the stress reaches steady state as the films planarize. With a fixed island size, increasing the growth rate causes an increase in the steady state stress, until a limiting value is reached at higher growth rates. The stress also shows some decrease with increasing island size. However, we observe a smaller grain size dependence than that predicted by previous theoretical models. To explain our results, a cohesive zone model of grain boundary formation is developed, in conjunction with a finite element analysis of the stress concentrations at the grain boundary cusps. This makes it possible to address both grain boundary phenomena and surface roughness effects.