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You can do a planet size comparison based on several criteria: mass, density, volume, or surface area. What you will find in this article is all four of those specs on each planet, then a comparison at the end.
Mercury has a mass of 3.3×1023kg, a density of 5.427 g/cm3, volume of 6.1×1010km3, and a surface area of 7.48×107km2.
Venus has a mass of 4.87×1024 kg, a density of 5.21 g/cm3, a volume of 9.38×1011km3, and a surface area of 4.6×108 km2.
Our planet has a mass of 5.97×1024kg, a density of 5.52 g/cm3, a volume of 1.08×1012km3, and a surface area if 5.1×108km2.
Mars has a mass of 6.42×1023kg, a density of 3.93 g/cm3, a volume of 1.63×1011km3, and a surface area of 1.4×108km2.
Jupiter has a mass of 1.9×1027kg, a density of 1.32 g/cm3, a volume of 1.43×1015km3, and a surface area of 6.22×1010km2.
Saturn has a mass of 5.69×1026 kg, a density of 0.687 g/cm3, a volume of 8.27×1014 km3, and a surface area of 4.27×1010 km2.
Uranus has a mass of 8.68×1025kg, a density of 1.27 g/cm3, a volume of 6.83×1013km3, and a surface area of 8.12×109km2.
Neptune has a mass of 1.02×1026kg, a density of 1.638 g/cm3, a volume of 6.25×1013km3, and a surface area of 7.64×109km2.
So, for the planet size comparison: the largest planet by mass is Jupiter, the largest by density is Earth, the planet with the highest volume is Jupiter, and the planet with the largest surface area is Venus.
We’ve also recorded a series of episodes of Astronomy Cast about every planet in the Solar System. Start here, Episode 49: Mercury.