To detect multiple paternity in highly fertile species, researchers commonly use the probability of detecting multiple mating (PrDM). Although the PrDM is a powerful tool to detect multiple paternity in a litter/brood/clutch, this analysis neglects the estimation of the statistical power at the population level. Here, we developed an analytical method to assess the statistical power to detect multiple paternity considering brood size and the number of females sampled in a population. The model tested with 1,000,000 of embryos per brood (as in marine crabs), different numbers of embryos per brood, and different numbers of females analyzed reached values of statistical power greater than 99% when the first male sired 90% of the progeny and 50% of females had multiple paternity. This analysis showed the importance of focusing on the experimental unit in the experimental design in studies where multiple paternity is being tested.