Boneyard Tools

Weight vs mass and how surface gravity works

Why your weight shifts from planet to planet while your mass stays fixed, and how surface gravity ratios turn one number into eleven.

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Mass is constant, weight is not

Mass is the amount of matter in your body, and it is the same whether you stand on Earth, float in orbit, or walk on Mars. Weight is different: it is the force gravity exerts on that mass, so it depends entirely on where you are. On Earth a kilogram of mass pushes down with about 9.81 newtons of force, but on the Moon the same kilogram pushes with only about 1.6 newtons. This calculator works in the everyday sense of weight, the number a bathroom scale would show, which is why the same person reads so differently from world to world.

What a gravity ratio really means

Each body in the table carries a surface gravity ratio with Earth set to 1. Mars sits at about 0.377, meaning its surface pull is roughly 38 percent of Earth's, while Jupiter at 2.36 pulls more than twice as hard. To find your weight anywhere you simply multiply your Earth weight by that ratio, which is exactly what the tool does behind the scenes. Because it is a pure multiplication, the unit you start with, pounds or kilograms, is the unit you end with.

Why the gas giants and the Sun are odd cases

Jupiter, Saturn, Uranus and Neptune have no solid ground to stand on, so their listed gravity is measured at the visible cloud tops rather than a real surface. Saturn is a surprise to many people: despite being enormous, its low density gives it a surface gravity of about 0.916, just under Earth's. The Sun's ratio of 27.9 produces huge numbers that are purely illustrative, since its heat and pressure make standing there impossible. Treat those figures as a fun sense of scale, not a travel plan.

Everyday uses for the numbers

Teachers use planet weights to make gravity concrete for students, and science museums print them on interactive scales. Writers and game designers reach for them to keep low gravity worlds believable. The quick rule of thumb worth remembering is the Moon at about one sixth and Mars at a bit over one third of your Earth weight, which covers the two destinations people ask about most.

Frequently asked questions

Would I feel lighter or just weigh less on Mars?

Both. Your muscles would lift your body against only about 38 percent of Earth's pull, so you would feel noticeably lighter and could jump much higher, while a scale would also read about a third of your Earth weight.

Does astronaut weightlessness mean zero gravity?

Not exactly. Astronauts in orbit still sit inside Earth's gravity, but they and their spacecraft are in continuous free fall around the planet, so there is no support force and scales read zero. That state is better called microgravity than zero gravity.