Earth is a substantial world, yet our perspective on its size changes dramatically when measured against the other seven major planets in the solar system. To understand where our home planet stands, we must look at the rocky worlds closest to the Sun and the colossal gaseous bodies that dominate the outer solar system. This comparison establishes Earth’s position within the planetary scale, revealing it to be neither the largest nor the smallest of the eight planets.
Measuring Planetary Size: Mass, Volume, and Diameter
Defining a planet’s size involves more than just measuring its width. Astronomers use three primary metrics: diameter, volume, and mass. Diameter is the distance measured straight across a planet through its center. This metric provides a simple comparison of a planet’s physical span.
Volume calculates the total amount of space a planet occupies. This metric determines how many times one planet could theoretically fit inside another.
A planet’s volume increases exponentially compared to its diameter. This means a small increase in diameter results in a vastly larger volume.
The final metric is mass, which represents the total amount of material contained within the planet. Mass dictates a planet’s density and the strength of its gravitational pull. Two planets can have similar diameters but widely different masses, indicating they are composed of entirely different materials.
Earth’s Place Among the Inner Rocky Worlds
Earth is the largest of the four terrestrial, or rocky, planets in the inner solar system. These planets—Mercury, Venus, Earth, and Mars—are relatively small, dense worlds compared to the outer giants. Earth serves as the standard against which the others are measured, placing it at the top of the terrestrial size chart.
Venus, the second planet from the Sun, is the closest in size to Earth. It has a diameter that is about 95% of Earth’s and a volume that is approximately 86% of our planet’s volume, earning it the nickname “Earth’s twin”. This similarity in size, however, belies a significant difference in atmospheric composition and surface conditions.
Mars is considerably smaller than both Earth and Venus. The Red Planet’s diameter is only about 53% that of Earth, and its volume is a mere 15% of Earth’s total volume. In terms of mass, Mars is only about one-tenth as massive as Earth.
Mercury, the planet closest to the Sun, is the smallest of all the major planets. Its diameter is just over one-third that of Earth, and its volume is only about 5.4% of Earth’s.
Earth’s Scale Next to the Gas Giants and Ice Giants
The scale difference between Earth and the four outer planets is immense. Jupiter, the largest planet, is a true behemoth of the solar system. Its diameter is more than 11 times greater than Earth’s, meaning 11 Earths could be lined up side-by-side across Jupiter’s equator.
The volume comparison is even more stunning, as Jupiter is so large it could contain approximately 1,321 Earths stacked inside it. Furthermore, the mass of Jupiter is nearly 318 times greater than Earth’s mass, making it more massive than all the other planets in the solar system combined.
Saturn, the second-largest planet, is slightly smaller than Jupiter but still dramatically larger than Earth. It is about 9.5 times wider than Earth, and its volume is large enough to hold about 764 Earths.
The two outermost planets, Uranus and Neptune, are referred to as ice giants and are roughly the same size. Uranus has a diameter about four times that of Earth, and Neptune is only marginally smaller. While smaller than Jupiter and Saturn, these ice giants still dwarf Earth, with the volume of Uranus being large enough to hold around 63 Earths. When all eight planets are ranked by size, Earth is found to be the fifth largest.