The growing interest in dark energy and dark matter has made studies on the energy density in the universe a very current topic. Furthermore, new cosmological measurements are calling into question the validity of the ΛCDM model, and it is necessary to review it in depth. To solve these new challenges, Professor Fulvio Melia has developed a linear expansion universe model, the Rh=ct universe, which is giving very good results in relation to the new cosmological measurements. In this report we have developed, within this model of the universe, an equation that allows us to calculate the value of the energy density as a function of the age of the universe. The result in reference to the current experimental value of the energy density obtained by Mission Planck coincides with the value obtained by our equation 0,97.10-26 Kg/m3. For this reason, we believe that our equation can be useful when determining energy densities of the universe at earlier and later times. With this wish we present our work.