This is the gravitational radius of an electron:

r_e = 2GM_d/(c²r)

where

G is Newton's gravitational constant,

M_d is the mass of the central body = 10⁻¹⁸kg,

c is the speed of light, and

r is the Bohr radius.

This gives a value

r_e = 10 ⁻¹⁵m