The general form for density D=M/V. Applying this formula to the Earth, DE=ME/VE. So, if V is the volume of a planet, V/VE is the proportion of its volume in relation to Earth. If the planet is bigger than Earth, then V/VE>1 and compressing its mass into the same volume as the Earth would increase its density by the same factor. So the density would change to D.V/VE. There would be a decrease in density if V<VE. But D=M/V, so the change in density would simply be M/VE. This is of course the mass of the planet squeezed or expanded into Eath's volume.

The density of water is 1g/cc=1E12kg/km^3. The density of the planets is best shown using the density of water as the unit. Treating every planet as a perfect sphere and knowing the mean radius of each we can work out the volume and calculate the density.

PLANET |
Radius (km) |
Mass (kg) |
Volume (km^3) |
Density (compared to water) |
Changed density |

Mercury |
2440 |
3.30E23 |
6.09E10 |
5.42 |
0.30 |

Venus |
6052 |
4.87E24 |
9.29E11 |
5.25 |
4.48 |

EARTH |
6378 |
5.97E24 |
1.09E12 |
5.49 |
5.49 |

Mars |
3397 |
6.42E23 |
1.64E11 |
3.91 |
0.59 |

Jupiter |
71492 |
1.90E27 |
1.53E15 |
1.24 |
1748 |

Saturn |
60268 |
5.68E26 |
9.17E14 |
0.62 |
523 |

Uranus |
25559 |
8.68E25 |
6.99E13 |
1.24 |
80 |

Neptune |
24766 |
1.02E26 |
6.36E13 |
1.60 |
94 |

Pluto |
1150 |
1.27E22 |
6.37E9 |
1.99 |
1.17 |