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Redmoon Calculators
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Sci-Fi Planet Gravity & Weight Converter

Calculatrice gratuite de gravité planétaire.

Quand l’utiliser

Use when building a sci-fi setting with multiple inhabited worlds. Gravity affects daily life, athletics, combat, and engineering — get the number first.

Comparaison

Real astrophysics calculators want SI units and rotational data. This is a writer's shortcut using Earth-relative inputs.

Enter your values below. Calculations run locally as you type.

Comment ça marche

In Earth-relative units, g = M ÷ R². A planet with twice Earth's mass but the same radius has 2g surface gravity.

Local weight = Earth weight × g. Vertical jump height = Earth jump ÷ g.

Above 1.5g, characters tire faster and fall damage increases proportionally.

Formule

FAQ

Does it model atmosphere?

No. It only computes surface gravity from mass and radius. Atmospheric effects need a separate model.

What's the formula?

g = G·M/R². In Earth-relative units this simplifies to mass / radius².

Why does radius matter more than mass for surface gravity?

Surface gravity follows g = G·M/R^2, so it scales linearly with mass but with the inverse square of radius. A planet twice Earth's mass but also twice its radius actually has half Earth's surface gravity.

Why does my weight change but my mass stay the same on another planet?

Mass is the amount of matter in your body and never changes with location, while weight is mass times local gravity. On a low-g world you weigh less because g is smaller, even though you contain exactly the same matter.

Exemple concret

Entrée

Mass 2× Earth, radius 1× Earth, 160 lb character.

Sortie

Surface gravity: 2.00 g. Local weight: 320 lb. Jump: 0.25 m.

g = mass/radius² = 2/1² = 2g. Weight scales linearly; jump height scales inversely.

Pièges courants

  • Atmosphere, magnetic field, and temperature aren't modeled.
  • Long-term human adaptation to non-1g environments is biologically complex.
  • Above ~3g, even healthy humans risk circulatory collapse.

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