Planet Size Comparison

What the planet size comparison shows

This tool draws the Sun, the eight planets, Earth's Moon and Pluto at a single consistent scale, so you can see how they really compare in size. Pick any two bodies and the larger one fills the frame while the smaller one is drawn at exactly the right proportion. The line-up view places all of them side by side on one scale. Every number comes from NASA's National Space Science Data Center (NSSDC) fact sheets, the same reference tables astronomers and educators use.

It is the largest-scale cousin of the site's 3D height comparison tool. Instead of comparing people measured in centimeters, it compares worlds measured in thousands of kilometers. The underlying principle is identical: put everything on one scale and the differences become obvious.

The numbers behind the drawing

The table lists the values the tool uses. Diameters are equatorial, in kilometers. Gravity is at the surface for rocky bodies and at the level where atmospheric pressure equals 1 bar for the giant planets, which have no solid surface.

The Sun's diameter is twice NASA's volumetric mean radius of 695,700 km. The NSSDC sun fact sheet lists its volume as 1,304,000 times Earth's, and NASA's public Sun facts page rounds that to 1.3 million Earths. The Sun also holds 99.8% of the solar system's mass.

How the to-scale drawing is built

Each body is a circle whose radius is proportional to its real radius. In the pair view, the larger body is drawn 240 pixels across and the smaller one is scaled from it. In the line-up, all eleven bodies share one scale, which creates a practical problem: if the Sun is a sensible size on screen, Pluto is a fraction of a pixel. The drawing therefore enforces a minimum on-screen size for the tiniest bodies so they remain visible, and the page notes this whenever it happens. Everything above that minimum is exact.

Volume ratios in the table and FAQs are the cube of the diameter ratio. Jupiter is 11.21 times wider than Earth, and 11.21 cubed is about 1,408, so roughly 1,400 Earths would fit inside it by volume if you could melt them down; real spheres leave gaps when packed, so you could fit fewer whole Earths. For gravity comparisons, the tool simply divides each value by Earth's 9.8 m/s².

Why distances are not to scale

Only sizes are drawn to scale. On the same scale, the distances would be absurd. Earth's average distance from the Sun, 149.6 million km, is about 107 Sun-diameters. Neptune, at 4,515 million km, sits about 3,245 Sun-diameters away. If the Sun in the line-up were the width of your screen, Earth would be a dot about a hundred screen-widths away and Neptune several kilometers off. Planetariums and printed posters squeeze planets together for the same reason.

Equatorial versus polar diameter

Planets are not perfect spheres. Rotation flings material outward at the equator, so every planet is slightly squashed, and the tool's choice of the equatorial diameter matters most for the fast-spinning giants. NASA's fact sheets give the details:

Earth's flattening is too small to see, a difference of about 21 km in radius. Saturn's is dramatic: its polar diameter is almost 11,800 km shorter than its equatorial diameter, enough to notice in a telescope. Jupiter, which completes a rotation in just 9.9 hours, bulges by about 4,600 km in radius. Because the tool draws circles from the equatorial diameter, the giant planets appear very slightly larger than their true average size; for Jupiter, NASA's volumetric mean radius of 69,911 km is about 2% smaller than the equatorial value.

The Sun is the one body where the tool uses the mean radius instead, since its shape is extremely close to spherical and NASA quotes its size as a volumetric mean.

How the largest moons measure up

The tool includes only Earth's Moon, but the comparison becomes more interesting with the solar system's other large moons. Diameters below are twice the radii in NASA's satellite fact sheets.

Ganymede and Titan are wider than the planet Mercury, but because they are made largely of ice and rock rather than dense rock and metal, they have much less mass. Size, again, is not the same as heft. Earth's Moon is unusual in a different way: relative to its planet, at about 27% of Earth's diameter, it is far larger than the major moons of the giant planets are relative to theirs.

Shrinking the solar system to human scale

Comparisons are easier to feel at a size you can hold. If Earth were a 1 cm marble:

At the same scale, Earth would orbit about 117 m from the Sun-ball, longer than a football field. That one image explains why spacecraft take months to reach Mars and years to reach the outer planets.

For a sense of how flat planets are on that scale, compare Earth's tallest mountain. The site lists Mount Everest at 8,848.86 m. Earth's diameter is 12,756 km, so Everest is about 0.07% of Earth's width; on the 1 cm marble it would be about 7 thousandths of a millimeter high, far smaller than a speck of dust. You can see Everest against human-scale landmarks on the Mount Everest page, and against the world's tallest buildings, such as the Burj Khalifa, on the landmarks hub.

Surprises that the scale drawing reveals

Venus is almost Earth's size. At 95% of Earth's width, it is the closest match in the solar system, yet its thick carbon dioxide atmosphere gives it the highest mean temperature of any planet, 464 °C per NASA.

Mercury is barely bigger than the Moon. At 4,879 km, Mercury is the smallest planet, only about 40% wider than the Moon.

Uranus and Neptune are near twins. They differ in diameter by only about 3%, but Neptune is denser and more massive, which is why its gravity (11.0 m/s²) is higher than Uranus's (8.7 m/s²).

Size is not the same as gravity. Saturn is more than nine times Earth's width, but its gravity at the cloud tops is slightly lower than Earth's because it is the least dense planet; the NSSDC lists its density at 687 kg/m³, lower than water. Gravity at the surface depends on mass divided by radius squared, so a huge, light planet can pull less than a small, dense one.

Pluto is smaller than the Moon. At 2,376 km, Pluto is about 68% of the Moon's diameter.

Your weight across the solar system

Because the tool shows gravity for each body, it is easy to translate into something personal. Your mass is the same everywhere, but the reading on a bathroom scale changes with gravity. For a person whose Earth scale reads 70 kg:

The giant-planet figures are a thought experiment, since there is no surface to stand on at the 1-bar level.

The Pluto question

Pluto is included because people constantly compare it with the planets and with the Moon. Since 2006 it has been classified as a dwarf planet. At its 26th General Assembly in Prague, on August 24, 2006, the International Astronomical Union adopted a definition with three criteria: a planet orbits the Sun, has enough mass for its own gravity to pull it into a nearly round shape, and has cleared the neighborhood around its orbit. Pluto meets the first two but shares its region of space with many other icy bodies in the Kuiper Belt, so it was placed in the new dwarf planet category. NASA's New Horizons spacecraft made the first close flyby in 2015. The scale drawing makes the classification debate concrete: Pluto is a tiny world, smaller than seven moons in the solar system, including Earth's.

Moon counts change, diameters do not

The diameters and gravities in this tool are stable measured quantities. Moon counts are not. The giant planets keep yielding small, irregular moons a few kilometers across, found with large ground-based telescopes and space telescopes. NASA's NSSDC fact sheet, used for the diameters and gravities on this page, lists 95 moons for Jupiter, 274 for Saturn, 28 for Uranus, 16 for Neptune and 5 for Pluto. NASA JPL's satellite discovery list, which records every satellite officially recognized by the International Astronomical Union, now shows 115 for Jupiter, 293 for Saturn and 29 for Uranus, and those are the counts in the table above. Neither source is wrong; the fact sheet is simply updated less often. Expect the JPL numbers to keep rising as new discoveries are confirmed.

Ways to use the comparison

The pair selector answers most size questions in two clicks, but a few combinations are especially revealing:

• Earth and Venus shows how similar two rocky planets can look in size while being utterly different worlds.
• Earth and the Moon gives the classic one-quarter ratio; try to guess how many Moons span Earth's width before you look (about 3.7).
• Jupiter and the Sun makes the Sun's dominance clear: the largest planet is only about a tenth of the Sun's width.
• Mercury and the Moon, then Moon and Pluto, walks down the small end of the scale and shows why Pluto's reclassification felt natural to many astronomers.
• Uranus and Neptune demonstrates how hard it is to tell the two ice giants apart by size alone.

For classrooms, the line-up view works well projected on a wall: ask students to rank the planets by size first, then reveal the drawing. Most people overestimate Mars and underestimate the gap between the rocky planets and the giants. Pair the drawing with the gravity column to discuss why a planet's size and its pull are related but not the same thing, and with the "Earth = 1 cm" table to turn abstract kilometers into objects on a desk. Because every value comes from NASA's published fact sheets, the numbers can be checked against the original tables, which also list density, escape velocity and orbital data for anyone who wants to go further.

When to use another tool

This page is for astronomical sizes. To compare people, characters or objects at human scale, use the 3D height comparison tool. To compare buildings, towers and mountains, browse the landmarks hub, and for ranked lists of tall things on Earth, from people to statues, see the tallest lists.