Calculate g of Another Planet
Instantly compute surface gravity or gravity at altitude using the standard gravitational formula. Select a known world like Mars, Jupiter, Titan, or the Moon, or enter custom mass and radius values for an exoplanet, dwarf planet, or fictional science project body.
- Uses the physical equation g = GM / r² with optional altitude.
- Supports preset planets and custom mass and radius units.
- Shows gravity in m/s², Earth g, and estimated 70 kg apparent weight.
Interactive Calculator
Choose a preset body or enter your own planetary mass and radius. If you add altitude, the calculator uses the distance from the center of the planet plus that extra height.
Results
Your calculated gravitational acceleration will appear below together with a visual comparison against Earth and selected benchmark worlds.
How to calculate g of another planet accurately
When people ask how to calculate g of another planet, they are usually asking for the local gravitational acceleration near that world. In physics, the symbol g represents the acceleration produced by gravity at a given distance from the center of mass. On Earth, the average surface value is about 9.81 meters per second squared, but other planets, moons, dwarf planets, and even large asteroids can have dramatically different values. The reason is simple: gravity depends mainly on two measurable properties, the body’s mass and the distance from its center. A massive planet tends to pull more strongly, while a larger radius spreads that mass farther from the surface and reduces the acceleration you feel there.
This matters in astronomy, aerospace engineering, human spaceflight, planetary geology, and education. If you are planning a classroom project, estimating how high a rocket could launch, comparing exoplanets, or simply wondering how much you would “weigh” on Mars or Jupiter, calculating g gives you the foundation. It affects jump height, falling speed, atmospheric retention, orbital mechanics near the surface, and the force that objects exert on the ground. Although the concept sounds advanced, the actual calculation is straightforward once the units are handled correctly.
In this equation, G is the universal gravitational constant, M is the mass of the planet or moon, and r is the distance from the center of that body to the location where you want gravity. At the surface, r is effectively the planetary radius. If you are above the surface, such as on a mountain, in the upper atmosphere, or in low orbit, then r becomes radius plus altitude. The calculator above handles this automatically for you, converting units and applying the formula directly.
Why mass alone does not tell the whole story
A common mistake is to assume that the most massive planet must always have the strongest surface gravity. That is not always true. Jupiter is much more massive than Earth and has stronger gravity at its cloud tops, but the difference is not as extreme as many people expect because Jupiter is also far larger. Surface gravity scales with mass divided by radius squared. If radius grows along with mass, the final value can remain moderate. This is why Saturn, despite its huge mass, has surface gravity surprisingly close to Earth’s value.
The reverse is also true for smaller bodies. Mars has only about 10.7% of Earth’s mass and roughly 53% of Earth’s radius, producing a surface gravity of about 3.71 m/s². The Moon is even lower at around 1.62 m/s². Pluto, despite being larger than many asteroids, still has very weak gravity because it has relatively low mass and a modest radius. Looking at both mass and radius at the same time is the only reliable way to compare worlds.
Step by step process for calculating planetary gravity
- Find the mass of the planet or moon in kilograms.
- Find the radius in meters, or convert it from kilometers.
- If needed, add altitude above the surface to the radius.
- Use the gravitational constant G = 6.67430 × 10-11 m3 kg-1 s-2.
- Apply the equation g = GM / r².
- Express the result in meters per second squared, and optionally divide by Earth’s 9.80665 m/s² to get Earth g.
For example, using Earth’s mass of about 5.9722 × 1024 kg and mean radius of 6,371,000 m, the formula gives approximately 9.82 m/s², very close to the standard Earth value. If you use Mars with a mass of 6.4171 × 1023 kg and a radius of 3,389,500 m, the result is about 3.73 m/s². Minor differences occur depending on whether you use equatorial radius, mean radius, polar radius, or accepted standard surface gravity values.
Important: “Weight” changes from planet to planet, but “mass” does not. A 70 kg person still has a mass of 70 kg on the Moon, Mars, or Jupiter. What changes is the gravitational force acting on that person, measured in newtons.
Comparison table: gravity across major solar system bodies
The table below gives representative mean values for mass, radius, and surface gravity for several well-known bodies. These numbers are useful for reality checks when you use the calculator. Values may vary slightly depending on source methodology and whether a mean, equatorial, or standard gravity is reported.
| Body | Mass (10^24 kg) | Mean Radius (km) | Surface Gravity (m/s²) | Relative to Earth |
|---|---|---|---|---|
| Mercury | 0.3301 | 2439.7 | 3.70 | 0.38 g |
| Venus | 4.8675 | 6051.8 | 8.87 | 0.90 g |
| Earth | 5.9722 | 6371.0 | 9.81 | 1.00 g |
| Moon | 0.07346 | 1737.4 | 1.62 | 0.17 g |
| Mars | 0.64171 | 3389.5 | 3.71 | 0.38 g |
| Jupiter | 1898.19 | 69911 | 24.79 | 2.53 g |
| Saturn | 568.34 | 58232 | 10.44 | 1.06 g |
| Uranus | 86.813 | 25362 | 8.69 | 0.89 g |
| Neptune | 102.413 | 24622 | 11.15 | 1.14 g |
| Pluto | 0.01303 | 1188.3 | 0.62 | 0.06 g |
| Titan | 0.1345 | 2574.7 | 1.35 | 0.14 g |
How altitude changes gravity
Gravity gets weaker as distance from the center of the planet increases. This does not mean gravity suddenly stops in orbit. In fact, astronauts in orbit are still strongly affected by Earth’s gravity. They experience apparent weightlessness because they are in continuous free fall around Earth. If you want to calculate g at an altitude, replace radius with radius plus altitude. Even a relatively small change in distance can produce a measurable difference, especially around smaller bodies.
Suppose a spacecraft is 400 km above Earth’s surface. The distance from Earth’s center becomes about 6,771 km instead of 6,371 km. Using the same formula, gravity drops from roughly 9.81 m/s² to about 8.69 m/s². That is still almost 89% of surface gravity. This is a useful reminder that orbital motion is not the same thing as escaping gravity.
Comparison table: estimated apparent weight of a 70 kg person
Because many readers think in terms of personal weight, the next table converts surface gravity into force on a 70 kg person. The values below use force in newtons, which is the correct physics measure. A bathroom scale that is calibrated for Earth would display a lower or higher “kg equivalent” depending on local gravity.
| Body | Surface Gravity (m/s²) | Force on 70 kg Person (N) | Earth Scale Equivalent |
|---|---|---|---|
| Moon | 1.62 | 113.4 | About 11.6 kg |
| Mars | 3.71 | 259.7 | About 26.5 kg |
| Earth | 9.81 | 686.7 | 70.0 kg |
| Saturn | 10.44 | 730.8 | About 74.5 kg |
| Jupiter | 24.79 | 1735.3 | About 176.9 kg |
Common unit conversions you must get right
- Kilometers to meters: multiply by 1,000.
- Earth masses to kilograms: multiply by 5.9722 × 1024.
- Jupiter masses to kilograms: multiply by 1.89819 × 1027.
- Earth radii to meters: multiply by 6,371,000.
- Jupiter radii to meters: multiply by 69,911,000.
Unit mistakes are by far the biggest source of error. If you accidentally use kilometers where meters are required, your result can be off by a factor of one million because radius is squared in the denominator. The calculator on this page reduces that risk by letting you choose common units from dropdown menus and converting them before solving.
What surface gravity means for life, exploration, and engineering
Surface gravity influences nearly every physical process on a planet. Lower gravity can allow taller mountains, slower sediment settling, reduced atmospheric pressure retention, and easier launch conditions for rockets. Higher gravity generally makes surface operations harder, increases structural loads, and changes how a human body moves. On worlds with very low gravity, dust can stay aloft more easily after impacts or landings. On higher gravity worlds, walking, lifting, and climbing become more demanding. For spacecraft design, g affects landing velocities, engine sizing, propellant needs, and habitat design.
Scientists also use planetary gravity to infer internal structure. If mass, radius, and density indicate a high concentration of metal, a world may have a large iron core. Combined with orbital data, gravity measurements help reveal subsurface oceans, mantle distribution, and the effect of rotation on planetary shape. That is why gravity is not just a classroom number. It is a key planetary diagnostic.
Frequently overlooked details
- Planets are not perfect spheres. Equatorial and polar radii differ, especially for rapidly rotating gas giants.
- Rotation changes effective gravity. At the equator, centrifugal effects slightly reduce what you feel.
- Atmospheric “surface” can be ambiguous. Gas giants do not have a hard solid surface like Earth or Mars.
- Mean gravity values are approximations. Local geology can alter gravitational measurements slightly.
- Exoplanet data often have uncertainty. Many published values are revised as better observations arrive.
Best sources for real planetary gravity data
If you want highly reliable reference numbers, consult official scientific sources. NASA’s planetary fact sheets provide widely used values for mass, radius, and other physical properties. The National Institute of Standards and Technology maintains accepted fundamental constants, including the gravitational constant used in the formula. NASA’s broader solar system resources also help explain how planetary properties are measured and updated over time. Recommended references include NASA planetary fact sheets, the NIST value for the gravitational constant, and NASA Solar System Exploration.
Using this calculator for custom planets and exoplanets
This calculator is especially useful when you want to estimate gravity for a body that is not listed in a standard textbook. For a custom world, all you need are mass and radius. If you are working from exoplanet catalog data, many sources report values in Earth masses and Earth radii. That makes comparison especially easy. A rocky super-Earth may have a much higher g than Earth if its radius does not increase as quickly as its mass. By contrast, a puffy gas giant can be extremely massive while maintaining only moderate surface gravity at a reference cloud level because its radius is enormous.
Keep in mind that “surface gravity” for exoplanets and gas giants is often more of a reference value than a practical standing surface. Still, the equation remains the same. As long as you know the mass and the distance from the center where you want the answer, you can calculate g.
Final takeaway
To calculate g of another planet, use one of the most important equations in astronomy and classical mechanics: gravitational acceleration equals the universal gravitational constant multiplied by planetary mass, divided by distance from the center squared. If you know mass and radius, you can estimate surface gravity in seconds. If you also know altitude, you can calculate local gravity above the surface just as easily. The interactive tool above streamlines the math, checks units, and gives you practical outputs such as Earth-relative gravity and apparent weight. Whether you are comparing Mars to Earth, exploring Titan, or building a fictional exoworld, the process is the same: convert carefully, apply the formula, and interpret the result in physical context.