In the theory of general relativity, it is possible to calculate the size and age of the cosmos using a new Einsteinian gravitational field equation. The equation describing the radius of the universe contains the mass of the Earth, of which the mass under certain conditions is equivalent to the mass of the cosmos. Looking back in time at the point when the universe was the same size as the Earth as a black hole, the mass of the Earth would increase in parallel with the universe’s decreasing size, in the end resulting in the total mass of the cosmos (5.4976•1053kg). Under these conditions, the average main mass density of the present cosmos would be 5.9814•10-26kg∙m-3. Using the masses calculated on the basis of the equatorial and polar radius of the Earth, it is possible to determine the ‘inside mass of the horizon of the cosmos’ in a figure of 2.9075•1051kg, when the mass density of the universe is 3.1634•10-28kg∙m-3. Solving the newfound equation for g, given that the size of the universe equals to that of the Earth as black hole, it is also possible to determine the total gravity of the primordial universe, which is 9.0273•1029m∙s-2. Replacing these results with the original equation, it is possible to determine both the initial radius and mass of the cosmos in figures of 1.5334•10-32m and 6.4877•10-5 kg (both ≈948.8 times the Planck length and Planck mass), while the primordial density is 4.29•1090 kg∙m-3. Under the premise of the above information, the time when the universe may have been formed can be calculated (5.1151•10-41s).