In simplest possible SIR model that takes into account the growing recovered and immune, (1 − 1/R0) of the population gets infected. R0 is the reproduction rate.

    R0 | % of population
    ----------------
    2.5  60% 
    2.0  50% 
    1.5  30%

The effective reproduction rate decreases when people take precautions. There is no reason to assume it's constant or same in different countries and cultures.