URANUS vs. MARS Uranus, the seventh planet from the sun, is more than 7 times the size of Mars, and almost 135 times as heavy. Here are some comparisons: Uranus' Radius: 25,559 km, 7.5 times as wide as Mars Uranus' Mass: 8.68 x 1025 kg, 135 times as massive as Mars. Uranus' Density: 1.32, 33% as dense as Mars.