Someone who has the will to look up in the net for physical data of the rocks, specifically the maximum load of compression per unit area (maximum pressure which it can sustain); then, fixed, let's say, one metre as the maximum height h of the asteroid's roughnesses and, let's say, 2000 kg/m

^{3} as typical rock's density rho, we can equal that max pressure with rho*g*h to find the maximum gravity g.

Edit: then, assuming a uniform composition and density (of course it would be just a rough approximation) it could be used the equation: g = k*r where r is the radius of the spherical asteroid and k the appropriate constant.

Edit2: assuming, just to see what comes out, 1 GPa as the plastic deformation load of a rock, the asteroid's radius should be 1 billion kilometres [

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Clearly, its average density couldn't be that at all...