How Big Is Earth Compared to Other Planets?

Earth’s Basic Measurements: A Benchmark in Space

To compare Earth with other planets, we first need to understand our planet’s own size metrics. Earth has an equatorial diameter of about 7,926 miles and a polar diameter of roughly 7,900 miles, due to its slightly flattened shape caused by rotation. Its total surface area spans about 197 million square miles, with 71% of that covered by water. Earth’s total volume is around 260 billion cubic miles, and its mass is approximately 5.97 × 10²⁴ kilograms. When measuring other planets, astronomers often use Earth as a baseline, applying units like “Earth diameters,” “Earth masses,” or “Earth volumes” to make comparisons more intuitive.

This baseline status also extends to gravity. Earth’s gravity is the standard we use to describe other planets’ gravitational strength. At the surface, Earth exerts a gravitational pull of 9.8 meters per second squared—enough to keep our atmosphere intact and our feet firmly planted on the ground. Compared to the solar system’s giants and dwarfs, Earth’s gravity and size are just enough to make it a goldilocks planet—not too big, not too small, and just right for life.

Mercury: The Tiny Messenger of the Solar System

Mercury is the smallest of all the planets, with a diameter of just 3,032 miles—less than half that of Earth. In terms of volume, Mercury could fit into Earth about 18 times. Its surface area is a mere 11% of Earth’s, and its mass is only about 5.5% of Earth’s mass. As a result, gravity on Mercury is only about 38% as strong as it is on Earth. That means you could jump more than twice as high on Mercury as you could on Earth. Despite being closest to the Sun, Mercury’s small size means it can’t hold onto an atmosphere, making it a barren, airless world. Compared to Earth, Mercury is a pebble, reminding us of the wide range of planet sizes even within the inner solar system.

Venus: Earth’s Twisted Twin

Venus is often called Earth’s sister planet because of its similar size and composition. Its diameter is about 7,521 miles—just 5% smaller than Earth’s. Venus has about 90% of Earth’s surface area and 86% of its mass. Its volume is roughly 85% of Earth’s, making it the most Earth-like planet in terms of physical size. But that’s where the similarities end. Venus is a world wrapped in thick clouds of carbon dioxide, with surface pressures over 90 times that of Earth and temperatures hot enough to melt lead. Despite its nearly identical size, Venus’s climate and conditions are drastically different, reminding us that size doesn’t determine habitability.

Mars: The Little Red Cousin

Mars, the fourth planet from the Sun, is noticeably smaller than Earth. Its diameter is 4,212 miles—just over half of Earth’s. Mars has only about 15% of Earth’s volume and 11% of its mass. Gravity on Mars is about 38% that of Earth’s, which is why future astronauts will feel much lighter on its surface. While smaller, Mars has about the same amount of dry land as Earth, since our oceans cover most of our surface. This makes Mars an intriguing candidate for future exploration and possible colonization. In planetary terms, Mars is like Earth’s leaner cousin—similar in some surface features, but much smaller overall in terms of planetary bulk.

Jupiter: The King of the Planets

Jupiter is the largest planet in the solar system by far, and it absolutely dwarfs Earth in every measurable way. With a diameter of 86,881 miles, Jupiter is more than 11 times wider than Earth. It is so large that more than 1,300 Earths could fit inside its enormous volume. Jupiter’s mass is 318 times that of Earth, and its surface gravity—if you could stand on its cloud tops—is about 2.5 times stronger. However, Jupiter doesn’t have a solid surface, being a gas giant composed mostly of hydrogen and helium. Its immense size contributes to its powerful magnetic field and the system of dozens of moons, including some that are nearly planetary in scale. Compared to Jupiter, Earth is a marble next to a basketball—a reminder of the true giants that orbit our Sun.

Saturn: The Elegant Giant

Saturn, known for its stunning ring system, is the second-largest planet in the solar system. It has a diameter of 72,367 miles, making it more than nine times wider than Earth. Its volume is so large that Earth could fit inside Saturn about 760 times. Yet Saturn’s mass is only 95 times that of Earth, and its gravity is slightly weaker than Jupiter’s—about 1.07 times Earth’s gravity at the cloud tops. This is because Saturn is the least dense planet; if you could find a bathtub big enough, Saturn would float in water. Despite its enormous size, Saturn is a delicate giant, with a lightweight composition and a ring system that spans over 170,000 miles in diameter. Earth, when compared to Saturn, feels almost fragile—a rocky core orbiting beneath the grandeur of gas and rings.

Uranus: The Tilted Ice Giant

Uranus is the third-largest planet in diameter, measuring about 31,518 miles—almost four times the width of Earth. It could fit about 63 Earths inside its volume. Uranus is an ice giant, composed largely of icy water, ammonia, and methane, giving it a pale blue-green color. Its mass is about 14.5 times that of Earth, and surface gravity is about 89% of Earth’s. Despite its large size, Uranus is extremely cold, with temperatures dipping below minus 370 degrees Fahrenheit. Its axial tilt is also extreme—about 98 degrees—causing the planet to essentially roll on its side as it orbits the Sun. Earth appears modest next to Uranus, both in size and planetary drama.

Neptune: The Windy Blue Giant

Neptune is similar to Uranus in size and composition. Its diameter is about 30,599 miles, roughly 3.9 times that of Earth. Neptune has about 58 times Earth’s volume and 17 times its mass. Gravity on Neptune is about 1.14 times stronger than Earth’s. While similar to Uranus in overall size, Neptune is far more dynamic, with the fastest winds recorded in the solar system, reaching up to 1,200 miles per hour. Its intense atmosphere of hydrogen, helium, and methane gives it a deep blue hue. Despite being over 2.7 billion miles from the Sun, its internal heat drives powerful storms and turbulence. Earth looks serene next to Neptune’s chaotic atmosphere and icy fury.

Earth in the Context of the Inner and Outer Planets

When we compare Earth to the inner and outer planets, we find that Earth is the largest of the rocky, terrestrial planets—Mercury, Venus, Earth, and Mars. These four worlds are all composed of rock and metal and have solid surfaces. In contrast, the outer planets—Jupiter, Saturn, Uranus, and Neptune—are vastly larger but lack a firm surface. They are composed of gas and ice, with atmospheres that stretch thousands of miles deep.

This division highlights an important point: Earth’s size isn’t just a number. It plays a critical role in the type of planet it is. Earth is large enough to retain a thick atmosphere, yet small enough to have a solid surface and manageable gravity. It sits at the perfect crossroads between the airless rocks of the inner system and the gas-swollen giants of the outer system.

Planetary Size and Habitability

Size plays a major role in determining a planet’s ability to support life. If Earth were smaller, it might not have enough gravity to hold onto its atmosphere or maintain liquid water on its surface. If it were much larger, it might resemble Neptune—a gas-covered world with no solid ground. Our planet’s size gives it a stable atmosphere, the right surface pressure, and a protective magnetic field generated by its molten core.

Mars, despite being a strong candidate for life, has lost most of its atmosphere due to its smaller size and weaker gravity. Venus, while similar in size to Earth, has developed a runaway greenhouse effect, likely due in part to its slow rotation and different atmospheric chemistry. Earth’s mass, size, and orbital position form a perfect synergy that makes it unique—not too big, not too small, and not too close or far from the Sun.

The Numbers Game: Why Size Isn’t Everything

While planetary size is a powerful indicator of physical characteristics, it doesn’t tell the whole story. Composition, atmosphere, temperature, and magnetic fields are just as critical in shaping a planet’s environment. Jupiter may be enormous, but it’s uninhabitable. Mercury may be close, but it’s a scorched wasteland. Mars may resemble Earth in some ways, but it lacks our atmosphere, magnetosphere, and hydrosphere.

Earth’s size puts it in a rare sweet spot. It’s large enough to be geologically active, supporting plate tectonics, volcanic activity, and a dynamic climate. These factors help recycle carbon, regulate temperature, and support life’s complex web. So while Earth may not win any prizes for sheer size, it wins where it counts.

Our Just-Right Planet

In the grand hierarchy of the solar system, Earth holds a unique position. It’s the biggest of the rocky planets, yet modest compared to the gas giants. It’s large enough to retain its atmosphere and magnetic field, yet small enough to have a solid surface and tolerable gravity. Earth’s size has shaped every aspect of our world—from the air we breathe to the water that covers our continents.

When we look at Mercury’s barren rock, Venus’s choking clouds, Jupiter’s stormy bulk, or Neptune’s icy winds, we gain a deeper appreciation for Earth’s balance. In the cosmic dance of the planets, size is more than just a number. It’s a key that unlocks the nature of a world. And Earth’s size, though unassuming next to the solar system’s titans, is exactly what made it the cradle of life. As we explore the planets near and far, Earth remains our benchmark—a blue world in a sea of extremes, perfectly shaped to be our home.