Using a proton charge 1.602*10^-19 coulombs is equal to proton mass 1.673*10^-27 Kg.
One coulomb = 1.673*10^-27 Kg divide by 1.602*10^-19
Therefore One coulomb is equal to 1.044*10^-8Kg.
Therefore One coulomb is approximately equal to a plank mass.
Knowing that the gravitation constant G used for calculating a plank mass relies on acceleration due to gravity g measured in a given location, the two should be the same.
https://en.wikipedia.org/wiki/Planck_mass
https://en.wikipedia.org/wiki/Gravitational_metric_system