Calculate an object's weight (gravitational force) from its mass, or its mass from a known weight, on Earth or other bodies in the solar system.
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Many people confuse mass and weight in everyday use, but they're physically different: mass is the amount of matter in an object, measured in kilograms, and it stays constant no matter where the object is. Weight, on the other hand, is the force of gravitational attraction (from Earth or any other planet) acting on that mass, measured in newtons (the SI unit of force), and calculated by the equation Weight = Mass × g, where g is the acceleration due to gravity (approximately 9.81 m/s² on Earth). This is why an object with a mass of 70 kg on Earth has exactly the same mass on the Moon, but its actual weight (the gravitational force on it) becomes much less there because the Moon's gravity is weaker (only 1.62 m/s²). This calculator lets you find weight from mass and a selected gravitational acceleration (Earth, Moon, Mars, Jupiter, or a custom value), or the reverse: finding mass from a known weight on that celestial body.
Everyday language treats mass and weight as interchangeable — we say someone 'weighs' 70 kilograms, mixing a mass unit with the concept of weight — but physics draws a sharp and important distinction between the two that becomes obvious the moment you leave Earth's surface.
Mass is a fundamental property of matter itself: the amount of physical substance in an object, which doesn't change based on location. A 70 kg astronaut has exactly 70 kg of mass whether standing on Earth, floating in the International Space Station, or standing on the Moon's surface — mass is intrinsic to the object, not dependent on its surroundings.
Weight is entirely different: it's the force that gravity exerts on that mass, and since gravitational acceleration varies dramatically between celestial bodies, weight varies right along with it even though mass stays fixed. The same 70 kg astronaut who weighs about 686 newtons on Earth (70 × 9.81) would weigh only about 113 newtons on the Moon (70 × 1.62), despite having identical mass in both locations.
This explains a detail that trips up many people: an astronaut on the Moon isn't 'lighter' in the sense of having less matter — they have exactly the same body mass, the same inertia, the same resistance to being pushed or accelerated. What's different is simply how strongly the Moon's weaker gravity pulls on that unchanged mass, which is why astronauts can jump so much higher on the Moon despite not having become physically smaller or less massive.
This distinction matters practically in aerospace engineering and mission planning, where spacecraft and equipment must be designed accounting for mass (which determines inertia, fuel requirements for acceleration, and structural loads during launch) separately from the weight the same equipment will experience on different planetary surfaces (which determines how much force landing gear, robotic arms, or astronaut mobility systems need to handle in that specific gravitational environment) — conflating the two concepts in engineering calculations would lead to serious design errors.
Mass is the amount of matter in an object, measured in kilograms, and stays constant everywhere; weight is the gravitational force acting on that mass, measured in newtons, and changes depending on the local gravitational acceleration.
Gravitational acceleration depends on a body's mass and radius — larger, denser bodies like Jupiter pull harder, while smaller bodies like the Moon pull much more weakly, which is why the same mass weighs less on the Moon than on Earth.
Strictly speaking no — kilograms measure mass, and the scientifically correct unit for weight (a force) is the newton; everyday scales actually measure mass and are calibrated assuming standard Earth gravity.