Planet Size Comparison: Every Planet From Smallest to Largest

Solar System · Planet sizes · Updated 2026-07-22

Ordered by diameter, the eight planets from smallest to largest are Mercury, Mars, Venus, Earth, Neptune, Uranus, Saturn, Jupiter. Mercury is the smallest at 4,879 km (3,032 mi) across and Jupiter is the largest at 142,984 km (88,846 mi), roughly 29 times Mercury's width and 11.2 times Earth's.

The chart below gives mean radius, equatorial diameter, and volume and mass relative to Earth in a single row per planet, plus Earth's Moon and Pluto as reference bodies. All figures are from the NASA Planetary Fact Sheet maintained by NASA Goddard Space Flight Center's National Space Science Data Center.

Planet size comparison chart, smallest to largest

Two columns are doing different jobs. Equatorial diameter is what almost every size chart quotes, and what you would measure across a photograph. Mean radius is the radius of a sphere of the same volume, which is the honest figure for the fast-spinning giants that bulge at the equator. For the rocky planets the two agree to within a kilometre or two; for Saturn they differ by more than 2,000 km.

The two real groupings

The eight planets do not form a smooth size gradient. They fall into two families with a wide, empty gap between them. Mercury, Venus, Earth and Mars are the terrestrial planets: rock and metal, all smaller than Earth or equal to it, all under 13,000 km across, with mean densities between 3,934 and 5,514 kg/m3. Nothing in this group reaches even 1.1 Earth diameters.

Jupiter and Saturn are the gas giants and Uranus and Neptune are the ice giants, made largely of hydrogen, helium, water, ammonia and methane. The smallest of the four, Neptune, is still 3.88 times Earth's diameter and 57.7 times its volume. That is the gap: step from Earth outward past Mars and the next planet you meet is nearly four times wider. Jupiter alone holds about 1,321 Earth volumes and 317.8 Earth masses, which is more than twice the mass of the other seven planets combined.

Why volume ratios are not diameter ratios cubed

This is where most size charts quietly go wrong. Volume scales with the cube of radius, so it is tempting to cube the diameter ratio. Cube Jupiter's equatorial diameter ratio of 11.209 and you get 1,408 Earth volumes. NASA lists 1,321. The 6.6% error comes from oblateness: Jupiter rotates once every 9.9 hours and its equator bulges outward, so its equatorial radius of 71,492 km is far larger than its polar radius of 66,854 km. Cube the volumetric mean radius ratio of 10.973 instead and you get 1,321, matching NASA exactly.

Saturn is worse. Cubing its equatorial ratio of 9.449 gives 844 Earth volumes, about 10% above the true figure of 764, which you recover by cubing its mean radius ratio of 9.140. Saturn's equatorial radius exceeds its polar radius by 5,904 km.

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Why Mercury is the smallest planet, not Pluto

Anyone who learned nine planets expects Pluto at the bottom of the list. Pluto was reclassified by the International Astronomical Union in 2006. IAU Resolution B5 defines a planet as a body that is in orbit around the Sun, has enough mass for its self-gravity to pull it into hydrostatic equilibrium (a nearly round shape), and has cleared the neighbourhood around its orbit. Pluto satisfies the first two and fails the third, so Resolution B6 classified it as a dwarf planet and the prototype of a new category of Trans-Neptunian Objects. The footnote to B5 names the eight planets outright.

The size argument was never the deciding one, but it is striking on its own. Pluto is 2,376 km across, barely half Mercury's width and roughly two-thirds the width of our own Moon. Two moons in the solar system are wider than Mercury:

Ganymede and Titan both beat Mercury on width and both lose badly on mass, because Mercury is rock and iron while they are substantially ice. Mercury is more than twice as massive as Ganymede despite being the smaller body. Width and heft rank these objects in opposite orders, which is the most useful thing any size chart can teach you.

Keeping the solar system in your pocket

A reference table answers one question and then closes. StarQuest is built for the other half: a daily fact from ten categories, including Solar System, delivered through Home Screen and Lock Screen widgets and on Apple Watch, with Favorites so the facts that land stay findable. No ads and no login, and the collections are there when you want to go deeper than one planet's diameter.

Frequently asked questions

What is the order of the planets from smallest to largest?

By diameter: Mercury (4,879 km), Mars (6,792 km), Venus (12,104 km), Earth (12,756 km), Neptune (49,528 km), Uranus (51,118 km), Saturn (120,536 km), Jupiter (142,984 km). Ordering by mass instead swaps Uranus and Neptune, since Neptune is heavier despite being narrower.

Is Pluto the smallest planet?

No. Pluto has not been a planet since 2006, when IAU Resolution B5 required a planet to have cleared the neighbourhood around its orbit and Resolution B6 reclassified Pluto as a dwarf planet. Mercury is the smallest of the eight planets. Pluto is 2,376 km across, about half Mercury's diameter.

How many Earths can fit inside Jupiter?

About 1,321 by volume, using NASA's figure of 143,128 x 10^10 km3 for Jupiter against 108.321 x 10^10 km3 for Earth. That is a pure volume ratio. If you actually packed rigid Earth-sized spheres inside Jupiter you would fit roughly 850 to 980, because spheres cannot fill a space completely: random close packing fills about 64% of a volume and the tightest possible arrangement about 74%.

How big is each planet compared to Earth?

By diameter, with Earth as 1: Mercury 0.383, Mars 0.532, Venus 0.949, Neptune 3.88, Uranus 4.01, Saturn 9.45, Jupiter 11.21. Only the four giant planets are larger than Earth, and Venus is the closest match to Earth at about 95% of its diameter and 82% of its mass.

Keep reading

• Hottest and Coldest Planets in the Solar System (Full Temperature Chart)
• How Many Moons Does Each Planet Have? Current Confirmed Counts
• The Biggest Star in the Universe: How the Largest Known Stars Compare to the Sun