The short answer: Neptune has a mass of about 1.02 × 1026 kg (roughly 2.25 × 1026 lb), which is around 17 times the mass of Earth.
Neptune weight by type
Neptune is the eighth and farthest planet from the Sun and is classified as an ice giant, made largely of water, ammonia, and methane ices.
| Comparison | Relative mass |
|---|---|
| Neptune mass | about 1.02 × 10²⁶ kg |
| Compared to Earth | about 17 times |
| Compared to Uranus | slightly heavier |
| Compared to Jupiter | about 5.5% of Jupiter |
What affects Neptune weight
- Ice and gas mix. Neptune's blend of icy materials and gas gives it substantial mass.
- Large size. As the smallest of the giant planets it is still about four times Earth's diameter.
- High density. Neptune is the densest of the giant planets at about 1.64 g/cm³.
- Rocky core. A dense core of rock and ice contributes to its overall mass.
- Measurement via moons. The orbit of its moon Triton helps astronomers calculate Neptune's mass.
How Neptune weight compares
Neptune is about 17 times heavier than Earth, making it slightly more massive than its near-twin Uranus despite being a bit smaller.
Frequently asked questions
Is Neptune heavier than Uranus?
Yes. Neptune is slightly more massive than Uranus at about 17 Earth masses versus roughly 14.5, even though Neptune is a little smaller. This makes Neptune the denser of the two ice giants.
Why is Neptune called an ice giant?
Neptune is called an ice giant because much of its mass consists of "icy" materials like water, ammonia, and methane, rather than the hydrogen and helium that dominate gas giants like Jupiter.
How was Neptune's mass measured?
Neptune's mass was determined by observing the orbit of its large moon Triton and by data from the Voyager 2 flyby in 1989. These observations reveal the planet's gravitational strength.
