Neptune
At the edge of the planetary realm.
How big is Neptune? Neptune is 49,528 km (30,775 miles) across at its equator — 3.88 times wider than Earth — and about 58 Earths could fit inside it. Gravity at the 1-bar level in its atmosphere is 11.0 m/s², 1.12 times Earth’s.
Neptune is a cold, windy ice giant far beyond the warmth of the inner solar system. It was found after calculations predicted where an unseen planet should be.
Image: NASA / JPL-Caltech; Voyager 2 (processed color). Processed mission imagery; apparent color varies with filters and processing.
Neptune quick facts
| Planet type | Ice giant |
|---|---|
| Equatorial diameter | 49,528 km (30,775 mi) |
| Mean radius | 24,622 km (15,299 mi) |
| Size compared with Earth | 3.88× as wide · 57.7× the volume |
| Equatorial circumference | 155,597 km (96,683 mi) |
| Surface area | 7.62 × 10⁹ km² |
| Volume | 6.25 × 10¹³ km³ |
| Mass | 1.02 × 10²⁶ kg (17.1 Earth masses) |
| Mean density | 1,638 kg/m³ (1.64 g/cm³) |
| Surface gravity | 11.0 m/s² (1.12× Earth) at 1 bar |
| Escape velocity | 23.5 km/s |
| Length of day (solar) | 16.1 hours |
| Rotation period (sidereal) | 16.1 hours |
| Orbital period (year) | 59,800 Earth days (163.72 Earth years) |
| Mean distance from the Sun | 4,515 million km (2,805.5 million mi) · 30.18 AU |
| Closest and farthest from the Sun | 4,471.1 – 4,558.9 million km |
| Distance from Earth | 4,319 – 4,711 million km |
| Sunlight travel time | 4 h 11 min |
| Mean orbital speed | 5.4 km/s |
| Axial tilt | 28.3° |
| Mean temperature | -200 °C at 1 bar |
| Known moons | 16 |
| Ring system | Yes |
Reference: NASA Planetary Fact Sheet. Rounded values; diameters are equatorial, area and volume use the mean radius. Moon counts include discoveries announced through 2025 (such as Uranus’s S/2025 U1) and keep growing as new moons are confirmed.
How big is Neptune compared to Earth?
Neptune’s equatorial diameter of 49,528 km makes it 3.88 times wider than Earth. By volume, about 58 Earths could fit inside it. Its mass is 17.1 times Earth’s, so its average density is similar: 1,638 kg/m³ (1.64 g/cm³).
Earth’s equatorial diameter is 12,756 km (7,926 miles). See every planet to scale ↗
What is the gravity on Neptune?
Gravity on Neptune is about 11.0 m/s² at the 1-bar level in its atmosphere: 1.12 times Earth’s 9.8 m/s². Someone who weighs 100 lb on Earth would weigh about 112 lb on Neptune. To escape its pull, a rocket needs 23.5 km/s.
Calculate your weight on Neptune ↗How far is Neptune from the Sun and Earth?
Neptune orbits an average 4,515 million km (2,805.5 million miles, 30.18 AU) from the Sun, ranging from 4,471.1 to 4,558.9 million km. Sunlight takes 4 h 11 min to get there. Its distance from Earth varies from about 4,319 to 4,711 million km.
Time sunlight’s journey ↗How long is a day and a year on Neptune?
A solar day on Neptune lasts 16.1 hours, and one spin relative to the stars takes 16.1 hours. A year — one trip around the Sun at 5.4 km/s — lasts 59,800 Earth days (163.72 Earth years). Its axis is tilted 28.3°.
Watch the orbit ↗Is Neptune a gas giant or an ice giant?
Neptune is usually called an ice giant rather than a gas giant. Like Jupiter and Saturn it has no solid surface, but more of its mass is made of “ices” — water, ammonia and methane — beneath a hydrogen–helium atmosphere. Uranus and Neptune are the two ice giants.
Meet all eight planets ↗Neptune questions, answered
How big is Neptune compared to Earth?
Neptune is 49,528 km (30,775 miles) wide at its equator, 3.88 times wider than Earth. By volume, about 58 Earths could fit inside it, and its mass is 17.1 times Earth’s.
What is the gravity on Neptune?
Gravity on Neptune is about 11.0 m/s² at the 1-bar level in its atmosphere, or 1.12 times Earth’s. Someone who weighs 100 lb on Earth would weigh about 112 lb there; escape velocity is 23.5 km/s.
What is the mass of Neptune?
Neptune has a mass of about 1.02 × 10²⁶ kg, or 17.1 Earth masses. Its mean density is 1,638 kg/m³ (1.64 g/cm³).
How far is Neptune from Earth?
The distance changes as both planets orbit the Sun. Neptune comes within about 4,319 million km of Earth and can be as far as 4,711 million km away. It orbits 30.18 AU from the Sun on average.
How long is a year on Neptune?
One orbit takes about 59,800 Earth days (163.72 Earth years). A solar day on Neptune lasts 16.1 hours.
Is Neptune a gas giant or an ice giant?
Neptune is usually called an ice giant rather than a gas giant. Like Jupiter and Saturn it has no solid surface, but more of its mass is made of “ices” — water, ammonia and methane — beneath a hydrogen–helium atmosphere. Uranus and Neptune are the two ice giants.
What is the density of Neptune?
Neptune’s mean density is 1,638 kg/m³ (1.64 g/cm³). Earth’s is 5,514 kg/m³.