It has been reported that the size and characteristics of ferroelectric domains which have an essential role on the ferroelectric properties depend on the grain size of ferrolectric ceramics. Therefore understanding the change of domain characteristics with grain size is so important to know the dependence of dielectric constant, dielectric loss and aging on the grain size. In this research, the equilibrim domain with is calculated as d={{{{ SQRT { { 64 pi sigma a} over {3C11Ss2 } } }}. This calculated value is nearly same to the measured value of BaTiO3 and Pb(Zr0.4Ti0.6)O3 ceramics 90$^{circ}$domain wall width. The calculated 90$^{circ}$domain wall enerygy in Pb(Zr0.4Ti0.6)O3 which is obtained through the model is approximately 2$ imes$10-2J/$m^2$.