Mass vs Weight Calculator
Find your weight (the force of gravity on your mass) on Earth or anywhere else in the solar system, and see how it compares across every planet.
Calculator verified • Last updated: August 2026
Mass & Location
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Your Weight Across the Solar System
Your mass never changes, but each bar shows how much you'd weigh if you stood on that planet's surface — driven entirely by differences in surface gravity. Notice how much lighter you'd feel on Mars or the Moon, and how much heavier on Jupiter or Neptune. Picking Custom adds its own bar so you can compare it directly against the rest.
Mass vs. Weight Explained
Mass and weight are often used interchangeably in everyday speech, but in physics they're fundamentally different quantities. Mass measures how much matter an object contains and never changes regardless of location. Weight is the force gravity exerts on that mass, and it depends on where you are.
W = mg
W: weight, in newtons (N).
m: mass, in kilograms (kg).
g: local gravitational acceleration, in meters per second squared (m/s²); about 9.81 on Earth's surface, but different on every other planet and moon.
Worked Example: 70 kg Person on Different Worlds
Using the calculator's default of a 70 kg person: on Earth (g = 9.81 m/s²), weight is 70 × 9.81 ≈ 686.7 N. On the Moon (g = 1.62 m/s²), the same 70 kg person weighs only about 113.4 N — roughly a sixth of their Earth weight, which is why astronauts could bound across the lunar surface in giant leaps. On Jupiter (g = 24.79 m/s²), that same person would weigh about 1735 N, more than double their Earth weight.
Why Gravity Differs From Planet to Planet
Surface gravity comes from Newton's Law of Universal Gravitation applied at a planet's surface:
g = GM/r²
g: surface gravitational acceleration, in meters per second squared (m/s²).
G: the gravitational constant, about 6.674 × 10⁻¹¹ N·m²/kg².
M: the planet's mass, in kilograms (kg).
r: the planet's radius, in meters (m).
A planet's surface gravity isn't just about how massive it is — it's a balance between mass and size. Mars has only about 11% of Earth's mass, but it's also much smaller, so its surface gravity works out to about 38% of Earth's rather than being ten times weaker.
A Brief History of Distinguishing Mass and Weight
Isaac Newton's Principia (1687) was the first to clearly separate mass, as a fixed measure of an object's inertia, from weight, as the force gravity exerts on it — a distinction not obvious before space travel and lunar exploration made it something people could actually observe firsthand. The clean separation became common knowledge largely after Apollo astronauts were filmed bouncing across the Moon in the 1960s and 70s, visibly weighing far less despite being made of exactly the same matter as on Earth.
Common Mass vs. Weight Mistakes
Saying "I weigh 70 kilograms" is the most common everyday mix-up — kilograms measure mass, not weight, and the actual weight equivalent is about 686 newtons. Assuming an astronaut in orbit is "weightless" because gravity vanishes in space is another common misconception; astronauts orbiting Earth are still in nearly the same gravitational field as the surface, they just experience apparent weightlessness because they're in continuous free fall. Confusing "heavier" gravity with "more massive" planet is a third common error, since gravity depends on both mass and radius together.
Using Pounds Instead of Kilograms
Switch the SI/Imperial dropdown above the mass input to enter your mass in pounds instead of kilograms. Weight is still calculated in newtons — and shown alongside in pound-force (lbf) — since surface gravity is defined in SI units regardless of which mass unit you're entering. Toggling converts whatever value is currently in the field rather than resetting it, so switching back and forth doesn't lose your number.
Mass and Weight Terms You Should Know
Mass — a measure of the amount of matter in an object, measured in kilograms, unchanged by location.
Weight — the gravitational force on a mass, measured in newtons, and dependent on local gravity.
Surface Gravity (g) — the gravitational acceleration at a planet or moon's surface, in m/s².
Apparent Weightlessness — the sensation of weightlessness experienced in free fall or orbit, even though gravity is still acting.
Surface gravity values used here are averages; actual local gravity varies slightly with altitude and geographic location, even on Earth.
Frequently Asked Questions
Why does my weight change but my mass stay the same?
Mass is a measure of how much matter you're made of, and that amount doesn't change no matter where you go. Weight is the force gravity exerts on that mass, and since different planets (and even different locations on Earth) pull with different strength, weight changes even though mass never does. Take a 70 kg person to the Moon and they're still 70 kg — they just weigh about a sixth as much.
Is a kilogram a unit of mass or weight?
A kilogram is a unit of mass, not weight — weight is a force and its correct SI unit is the newton. In everyday speech people say "I weigh 70 kilograms," which is technically describing mass, not weight; the actual weight of a 70 kg person on Earth is about 686 newtons.
Why is gravity different on other planets?
Surface gravity depends on both a planet's mass and its radius — specifically, g = GM/r², so a more massive planet pulls harder, but a larger radius puts you farther from its center and weakens the pull. Jupiter is far more massive than Earth but also much larger, so its surface gravity ends up only about 2.5 times Earth's, not enormously more.
Can I enter my mass in pounds instead of kilograms?
Yes — switch the SI/Imperial dropdown above the mass input. Weight is still calculated in newtons (with a pound-force equivalent shown alongside), since surface gravity values are defined in SI units, but the mass field itself accepts pounds and your currently entered value is converted rather than reset when you switch.