In recent years, novel devices which use nanomagnets to store and transmit information have been a particular topic of interest. Many of these devices utilize dipolar coupling between nanomagnets to process or communicate information and the most important factor when designing these systems is knowing if two nanomagnets are perfectly coupled . However, when modeling these devices, these nanomagnets are typically modeled as single-domain objects even though in many cases, the magnet dimensions far exceed the exchange length . While it is expected that very small magnets can be treated as single-domain objects, it is not quite clear how small is small enough. Second, it is not clear whether using a single-domain analysis underestimates or overestimates the coupling. In this work, we quantify the coupling between nanomagnets while considering their multi-domain behavior. Our simulations conclusively prove that ignoring multi-domain effects beyond a certain size yields inaccurate results. While the single-domain assumption predicts similar coupling strength to the multi-domain models for thin-film magnets with areas smaller than 1 μm2, the two models disagree about the coupling strength between larger magnets.