Planet Size Comparison

Our Solar System's eight planets divide neatly into two groups. The four inner worlds — Mercury, Venus, Earth and Mars — are rocky and small. Beyond the asteroid belt lie four giant planets: the gas giants Jupiter and Saturn, and the ice giants Uranus and Neptune.

Jupiter's equatorial diameter of roughly 143,000 km is about eleven times Earth's. Saturn is a little smaller. Uranus and Neptune are almost twins at around four Earth diameters across. Every gas- or ice-giant "surface" quoted in a fact sheet is defined at a chosen atmospheric pressure level, not a solid crust — their atmospheres deepen smoothly into supercritical fluid interiors.

The rocky planets almost disappear

Mercury is only 4,880 km wide. That makes it smaller than Jupiter's moon Ganymede and Saturn's moon Titan. Earth (12,756 km) is the largest terrestrial world; Venus is just slightly smaller. Mars, at 6,792 km, is roughly half Earth's diameter.

Why most Solar System diagrams cheat

When artists draw all eight planets on one page, Jupiter dwarfs the inner worlds so heavily that Mercury becomes a single pixel. Most educational graphics silently scale the terrestrial planets up. The diagram above is honest at a single scale, but adds a zoomed panel so the rocky planets remain readable on mobile.

What size does not tell you

Diameter is not the same as mass or density. Saturn is almost as wide as Jupiter but about a third of its mass — its bulk density is lower than water. Ice giants are denser than gas giants because they contain a larger fraction of water, methane and ammonia ices under high pressure. For the full picture, always compare diameter, mass and densitytogether.