I believe you are looking for hydrostatic equilibrium. There don’t seem to be good answers for this online, but according to Robert Black on this Quora post:
There isn’t a minimium per se but the generally accepted number for a mass to form into a sphere under its own gravity is 1/10,000th the mass of the Earth or 600 quintillion kg. As for size, it really depends on the composition of the body. The numbers are generally accepted to have a diameter of about 600km for a rocky body.
A quintillion is 1 x 10 to the 18th and Phobos has a mass of 1.0659 x 10 to the 16th kilograms and a diameter of 22 kilometers.
Phobos is this big and still not round? Uh, what was the name, the size where stone behaves like a liquid. Well, Phobos doesn’t have that yet?
Phobos is tiny. It’s just very close compared to our moon. 9500km as compared to our 384000km.
And the sun looks smaller from Mars because it’s further away, making Phobos seem bigger
Ah, thanks! Also, Phobos is fast!
I believe you are looking for hydrostatic equilibrium. There don’t seem to be good answers for this online, but according to Robert Black on this Quora post:
A quintillion is 1 x 10 to the 18th and Phobos has a mass of 1.0659 x 10 to the 16th kilograms and a diameter of 22 kilometers.
Yes that, thanks!