This paper is concerned with the discovery of a new theoretical formula for the mass of the proton. The latest and most accurate value of G obtained so far comes from atomic interferometry. This new and revolutionary experimental method was devised by an Italian team of scientists and the results were published in Nature in 2014. Due to the previous lack of accuracy and large discrepancies in the measurement of G, this experimental result is a scientific breakthrough that allow us and shall allow us to confirm, among other things, the validity of equations for the mass of particles, the latest fundamental particle formulations and cosmological theories. Since the equation presented here depends, among other things, on the gravitational constant G, I found that if we use the value of G given by NIST (2010), the formula reproduces the value of the proton mass accurate to three decimal places. If, on the other hand, we use the value of G given by the arithmetic mean published by Rosi et al, the formula reproduces the value of the proton mass accurate to four decimal places. Finally I found that, if we use the theoretical value of G of 6.671 614 932 ×10−11 m^3 Kg^−1 S^−2 (calibration value), the formula reproduces the value of the proton mass accurate to nine decimal places. This calibration value falls within the limits imposed by the experimental errors.