A mathematical model for estimating of the population size of West Bank and Gaza Strip is used. This model was first proposed in 1992. At that time there was no national, independent or reliable census there. Applying our (same) model showed a great deal of agreement, between our estimates for population size with the resulting figures of recent censuses, not only for these two areas, but for different countries worldwide. Testing and applying our model on accurate demographic data, from selected countries worldwide, with an emphasis to the Palestine case, shows its reliability and thus, its general validity. Background: so far, costly and lengthily census is the only way to estimate population size worldwide. So, there is a massive need to find a simpler and a more convenient alternative, a mathematical model; which saves time and reduces costs. Objective: To establish an independent source and framework for data on demography; alternative workable, and practical mathematical model that can be generalized, to cater different cases globally, to come up with and to produce real and true data for policy planners, and decision makers anywhere in the World, and to save time and reduce costs, substantially. Method: Deriving a mathematical model, based on considering a population process as a stochastic one, finding the moment-generating function and the expected value of the proposed population size. Results: population size estimates were calculated, by using simple calculating mathematical formulae. Conclusion: our general mathematical model can be useful and reliable alternative for traditional censuses anywhere worldwide.