Well, more or less, the size of a planet... :) There are fu*** big asteroids out there that aren't big enough to get spherical shape. Also, it will help if most of the planet is gas or liquid.

You can calculate the forces classically by Newton's expression for gravitational force: $$\vec F=-G\frac{Mm}{r^2}\vec u_r$$

$G$ is Newton's constant: $G\approx6.67\cdot 10 ^{-11}$ in IS units. You can see it's really week, compared to the constant of electrical force: $k\approx 9\cdot10^9$.
$M  $ and $m$ are the two masses between you want to calculate the force. $r$ is the distance between them. $-\vec u_r$ indicates the force is attractive.

So, the size of the person, well, a million things happens before the size is big enough to collapse in a sphere, like broken bones. You would need to know how resistent tissues are before they brake and so no, but I would go for a good approximation, that it's the order of the size of the moon (probably less than that), like 2 or 3 orders og magnitude smaller.

So gravity turns things round
Is saying things that would otherwise be considered loshon hara permitted in the context of mental health therapy? 

I am not familiar with the details of therapeutic schools, but I understand that some are predicated on an idea of speaking "freely" and exhaustively about the topics of therapeutic interest. Are there opinions that allow all speech within these contexts, understanding that the goal is the improvement of health and possibly the preservation of life?
