IIRC a sphere of neutronium about 150M in diameter is equivalent to the mass of the Earth. Of course, if you had one of those spheres it'd blow up in your face

IIRC a sphere of neutronium about 150M in diameter is equivalent to the mass of the Earth. Of course, if you had one of those spheres it'd blow up in your face and ruin your day. Probably wreck a bunch of the solar system, too.