Abstract. -Using the relation proposed by Weinberg in 1972, combining quantum and cosmological parameters, we prove that the self gravitational potential energy of any fundamental particle is a quantum, with physical properties independent of the mass of the particle. It is a universal quantum of gravitational energy, and its physical properties depend only on the cosmological scale factor R and the physical constants h and c. We propose a modification of the Weinberg´s relation, keeping the same numerical value, but substituting the cosmological parameter H/c by 1/R. Keywords: Cosmology, quantum mechanics, gravitational energy, cosmological scale factor, Weinberg´s relation.In 1972 Weinberg [1] advanced a clue to suggest that large numbers are determined by both, microphysics and the influence of the whole universe. He constructed a mass using the physical constants G, h, c and the Hubble parameter H. This mass was not too different from the mass of a typical elementary particle and is given by m ≈ (h 2 H/Gc) 1/3 (1)We consider also a general elementary particle of mass m. The self gravitational potential energy E g of this quantum of mass m (and size its Compton wavelength h/mc) is given by