Gravity on Neptune: how strong is it compared with Earth?

Neptune holds 17 times Earth’s mass, yet at its reference level the pull is only about 15% stronger than ours, because that mass is spread through a planet almost four times wider.

Gravity on Neptune averages 11.27 m/s², about 1.15 times Earth’s 9.82 m/s², according to NASA’s Neptune fact sheet. At the equator, where the planet’s spin works against gravity, NASA lists 11.00 m/s² (1.12 times Earth’s). A person whose bathroom scale reads 70 kg on Earth would see about 80 kg on the same scale at Neptune.

There is a catch in the word “surface”. Neptune has no solid ground, so these numbers apply at the height in its atmosphere where the pressure equals 1 bar, roughly the air pressure at sea level on Earth.

Explain it like I’m busy:

• Neptune’s gravity is 11.0 to 11.4 m/s² depending on latitude, about 1.12 to 1.16 times Earth’s.
• It has 17 times Earth’s mass but 3.9 times Earth’s radius, and gravity weakens with the square of the distance from the centre.
• You couldn’t stand there: the 1-bar level is cold gas at about −201 °C, with no floor beneath it.

Key facts about Neptune’s gravity

• Mean gravity: 11.27 m/s² at the 1-bar level, 1.15 times Earth’s (NASA NSSDCA).
• Equator vs pole: 11.00 m/s² at the equator and 11.41 m/s² at the poles, a spread of about 3.7%. Earth’s spread is about 0.5%.
• Mass and size: 1.02409 × 10²⁶ kg (17.15 Earths) and a mean radius of 24,622 km (3.865 Earths).
• Escape velocity: 23.5 km/s, about 2.1 times Earth’s 11.19 km/s.
• Among the planets: Neptune’s mean gravity is the second strongest at the 1-bar level, behind only Jupiter’s 25.92 m/s², and just ahead of Saturn’s 11.19 m/s².

What 11.27 m/s² would feel like

A dropped ball near Neptune’s 1-bar level would gain about 11.3 m/s of downward speed every second, compared with about 9.8 m/s on Earth. That is a 15% increase, not a crushing one.

For a 70 kg adult, the extra pull is like carrying about 10 kg more than usual, roughly a full suitcase of cabin luggage. The comparison has a limit. A suitcase loads your arms or shoulders, while stronger gravity pulls evenly on every part of you, including your blood and inner ear, so walking, standing and lifting your arms would all feel heavier at once.

Your mass would still be 70 kg. What changes is weight, the force gravity exerts on that mass: about 789 newtons on Neptune against 687 newtons on Earth (70 kg × 11.27 m/s² and 70 kg × 9.82 m/s²).

Source: NASA NSSDCA Neptune and Earth fact sheets. Weight = 70 kg × g. Scale readings are SciQuest calculations: 70 kg × (Neptune g ÷ Earth g at the same latitude type; the equator row uses Earth’s equatorial 9.78 m/s² and the pole row Earth’s polar 9.83 m/s²).

Why 17 Earth masses gives only 1.15 times the gravity

Surface gravity follows Newton’s law of gravitation:

g = GM/R²

G is the gravitational constant, M the planet’s mass and R the distance from its centre. Mass pushes gravity up in direct proportion. Radius pulls it down with its square, so a planet 3.865 times wider than Earth dilutes its pull by 3.865², or about 14.9.

In ratio form, using NASA’s Neptune-to-Earth ratios: 17.15 ÷ 3.865² = 17.15 ÷ 14.94 ≈ 1.15. That matches NASA’s listed ratio for mean gravity.

Another way to see it: for a sphere, g is proportional to average density times radius. Neptune is 3.865 times wider than Earth but only 0.297 times as dense on average (1,638 against 5,513 kg/m³), and 3.865 × 0.297 ≈ 1.15. Most of Neptune’s bulk is light hydrogen, helium and a hot, dense fluid of what NASA calls “icy” materials such as water, methane and ammonia, wrapped around a small rocky core.

How scientists know Neptune’s gravity

Nobody has dropped a ball on Neptune. Scientists measure the planet’s gravitational parameter, GM, by watching how things orbit it, then divide by the radius squared.

Step 1: weigh Neptune with its largest moon

Triton circles Neptune every 5.876854 days at an average distance of 354,760 km, according to NASA’s Neptunian satellite fact sheet. Kepler’s third law, as refined by Newton, turns those two numbers into GM:

GM = 4π²a³ ÷ T² = 4π² × (3.5476 × 10⁸ m)³ ÷ (507,760 s)² ≈ 6.837 × 10¹⁵ m³/s²

That SciQuest check lands within 0.03% of NASA’s value of 6.8351 × 10¹⁵ m³/s². NASA’s figure is more precise because it comes from fuller orbit modelling. JPL lists its Neptune mass as coming from R. A. Jacobson’s 2009 study of the orbits of Neptune’s satellites in The Astronomical Journal. The closest look so far came from Voyager 2, the only spacecraft to visit Neptune, which flew about 4,800 km above the cloud tops on 25 August 1989.

Step 2: divide by the radius squared

Using NASA’s GM and radii (1 km = 1,000 m):

Source: NASA NSSDCA Neptune fact sheet (GM = 6.8351 × 10¹⁵ m³/s²; radii at the 1-bar level). The middle column is a SciQuest calculation; check: 6.8351 × 10¹⁵ ÷ (2.4622 × 10⁷)² = 6.8351 × 10¹⁵ ÷ 6.0624 × 10¹⁴ = 11.27.

The mean value matches NASA exactly. At the equator and poles the simple formula is slightly off, for two reasons covered next: spin, and the way a squashed planet’s mass is arranged.

What changes the answer: 11.15, 11.0 or 11.27?

Search for Neptune’s gravity and you will find several numbers. They are all reasonable; they answer slightly different questions.

• 11.15 m/s² is GM divided by the equatorial radius squared, with no allowance for spin. NASA JPL’s planetary physical parameters page lists this as Neptune’s equatorial gravity, derived from mass and equatorial radius. Divided by Earth’s 9.80 m/s² on the same page, it gives the widely quoted 1.14.
• 11.0 m/s² (11.00 on the Neptune fact sheet) is NASA NSSDCA’s equatorial value including the effect of rotation. The NSSDCA planetary fact table defines its gravity column this way.
• 11.27 m/s² is NSSDCA’s mean value: GM divided by the volumetric mean radius squared. It is the best single “average” number, and it gives the ratio 1.15.
• 11.41 m/s² is the value at the poles, where there is no spin effect and you sit closest to the centre.

A practical rule: quote 11.27 m/s² (1.15 g) as the average, or 11.0 m/s² (1.12 g) if you mean the equator. Mixing methods causes errors. Some comparison lists put Neptune’s no-spin 11.15 beside Uranus’s with-spin 8.69, which overstates the gap between the two ice giants.

How Neptune’s 16-hour spin lowers equatorial gravity

Neptune turns once every 16.11 hours (a period NASA’s fact sheet notes was set from Voyager 2’s magnetic field measurements). At the equator, that spin flings you outward with an acceleration of ω²R:

ω = 2π ÷ (16.11 × 3,600 s) = 1.083 × 10⁻⁴ rad/s, so ω²R = (1.083 × 10⁻⁴)² × 2.4764 × 10⁷ m ≈ 0.29 m/s².

Subtracting that from 11.15 gives about 10.86 m/s², within about 1.3% of NASA’s 11.00. The rest comes from Neptune’s flattened shape. The planet bulges at the equator (its polar radius is 423 km shorter), and that extra equatorial mass adds a little pull at the equator and takes a little away at the poles compared with a perfect sphere. That is also why the simple polar figure of 11.54 m/s² sits above NASA’s 11.41. NASA’s tabulated values include these shape effects; our sphere-based arithmetic only approximates them, and we could not reproduce NASA’s equatorial figure to the last digit from fact-sheet numbers alone.

How Neptune compares with Earth and the other giants

Source: NASA NSSDCA fact sheets for Earth, Uranus, Neptune, Saturn and Jupiter. Equator and pole values include rotation.

Two comparisons stand out. Neptune is slightly smaller than Uranus yet has about 18% more mass, so its gravity is about 25% stronger (11.27 against 9.01 m/s²). And Neptune out-pulls Saturn at the equator (11.00 against 8.96 m/s²) despite having less than a fifth of Saturn’s mass. Saturn is the least dense planet, spins in about 10.7 hours and bulges strongly, which weakens its equatorial gravity; see our explainer on how strong gravity is on Saturn. For every planet and major moon side by side, use our guide to gravity on other planets.

Escape velocity: where Neptune’s mass does show

Escape velocity depends on GM/R rather than GM/R², so Neptune’s big radius hurts it less. From the equatorial 1-bar level:

v = √(2GM/R) = √(2 × 6.8351 × 10¹⁵ ÷ 2.4764 × 10⁷) ≈ 23,500 m/s = 23.5 km/s, about 2.1 times Earth’s.

So Neptune feels only a little heavier underfoot than Earth, but leaving it would take more than twice the launch speed.

Why it matters to you

Nobody will stand on Neptune, so this won’t change anything in daily life. What it teaches is a rule that works everywhere: surface gravity depends on mass and size, not mass alone. The same reasoning explains why Mars, with about a tenth of Earth’s mass, still has 38% of Earth’s gravity, as our Mars gravity explainer shows.

It also matters for anyone planning a mission. A spacecraft heading to Neptune has to account for a planet with 2.1 times Earth’s escape velocity, about 30 times farther from the Sun than Earth. Voyager 2 took 12 years to get there; see how long it takes to get to each planet.

“But wait… if there’s no surface, what happens if you fall in?”

You would keep falling. At the 1-bar level NASA’s fact sheet gives a temperature of about 72 K (−201 °C) and a gas density of only 0.45 kg/m³, a little over a third of the density of air at sea level on Earth. Below that the pressure keeps rising; NASA lists Neptune’s “surface pressure” simply as far more than 1,000 bars, because no true surface has been located.

The 1-bar level is therefore a convention, not a floor. Scientists chose it so that radius, gravity and escape velocity can be compared fairly across Jupiter, Saturn, Uranus and Neptune. Anyone imagining “standing on Neptune” is really imagining hovering, perhaps in a balloon, at that pressure level.

Related questions

Is Neptune’s gravity stronger than Earth’s? Yes, slightly: about 1.15 times on average and 1.12 times at the equator.

Does Neptune have stronger gravity than Uranus? Yes, about 25% stronger on average (11.27 against 9.01 m/s²), because Neptune packs more mass into a slightly smaller ball.

Which planet has gravity closest to Earth’s? At the mean values, Uranus (9.01 m/s²) and Venus (8.87 m/s²) are closest, each about 0.9 g. Read more in our explainer on gravity on Venus.

Which planet has the strongest gravity? Jupiter, at 25.92 m/s² on average, about 2.6 times Earth’s. See how strong gravity is on Jupiter.

In one sentence

Neptune pulls only about 15% harder than Earth (11.27 m/s² on average, 11.0 at the equator) because its 17 Earth masses are spread through a planet nearly four times wider, and the “surface” where that is measured is a pressure level in the clouds, not ground.

Read next

• Gravity on other planets: surface gravity of planets and major moons
• How strong is gravity on Saturn? Near Earth’s, from equator to pole
• How long does it take to get to each planet?

Disclosure: This article was drafted with AI assistance and checked against the sources below. The gravity, spin, escape-velocity, Triton-orbit and weight calculations are SciQuest calculations from NASA data, and the chart is an original SciQuest graphic. Spotted an error? See our corrections policy.

Sources

1. NASA NSSDCA, Neptune Fact Sheet (mass, GM, radii, gravity, escape velocity, rotation, 1-bar conditions)
2. NASA NSSDCA, Earth Fact Sheet
3. NASA NSSDCA fact sheets for Uranus, Saturn and Jupiter
4. NASA NSSDCA, Planetary Fact Sheet and Planetary Fact Sheet Notes (definition of equatorial gravity including rotation, 1-bar convention)
5. NASA NSSDCA, Neptunian Satellite Fact Sheet (Triton’s orbit)
6. NASA JPL Solar System Dynamics, Planetary Physical Parameters (11.15 m/s² equatorial value; mass source)
7. R. A. Jacobson (2009), The orbits of the Neptunian satellites and the orientation of the pole of Neptune, The Astronomical Journal 137, 4322–4329
8. NASA Science, Neptune: Facts (no solid surface, interior)
9. NASA Science, Voyager 2 (25 August 1989 flyby)