World
What If Earth Was Twice as Large?
Short answer: it depends what you keep the same. Keep the density and surface gravity doubles; keep the mass and it drops to a quarter. Pick the assumption below and see your weight and escape speed change.
If Earth's radius grew, what happens to surface gravity — same density or same mass?
'Twice as large' is not one question. Same stuff, bigger ball: mass grows with the cube of radius and surface gravity grows with radius. Same mass, stretched into a larger sphere: gravity at the surface falls as one over radius squared. Those two stories feel like opposites because they are. Escape speed follows yet another pairing: it scales with R at fixed density and with 1/√R at fixed mass. This page makes you pick the assumption, then shows g, weight, and escape speed. It will not build a new atmosphere or decide whether the core still convects. It will refuse to hide which knob you turned.
Written and checked by Aivora Digital · Last updated:
Change this
Results update as you move the controls.
This choice flips whether g goes up or down.
Your result
19.64 m/s²
surface g (same density)
2 × Earth in this mode
- Radius
- 12,742 km
- Mass
- 4.78 × 10^25
- Surface g
- 19.64 m/s²
- Your weight
- 1,473 N
- Escape speed
- 22,372 m/s
2 × mean Earth
scaled with R³
150.2 kgf
What does that mean?
Radius × 2 at the same density means mass × 8 (the cube). Surface g is 19.64 m/s², about 2× Earth, so a 75 kg body weighs 1,473 N instead of 735 N. Escape speed is 22,372 m/s (Earth's is about 11,186 m/s). You asked for a bigger world made of the same stuff; it holds you harder.
At a glance
- g on Earth9.82 m/s²
- g in this run19.64 m/s²
Compare
| Mode | same density |
|---|---|
| g vs Earth | 2× |
| Escape vs Earth | 2× |
Compare scenarios
Same density: g scales with R
Surface gravity is GM / R². Mass of a uniform ball is density times 4πR³/3, so g = (4π/3) G ρ R. Double the radius at the same density and you double g. You also multiply mass by eight. Standing on that world is a 2 g problem, which the gravity-doubled experiment treats in more personal units. Escape speed scales with R as well. This is the 'more planet' reading of the title.
Same mass: g falls as 1/R²
Hold M fixed and spread it. Double R and g drops by four; triple R and g drops by nine. Escape speed falls as 1/√R. The surface is farther from the same mass, so it holds you more gently and it holds air more gently too — a reminder that 'larger' can mean 'nearly uninhabitable for lack of gravity,' depending on the assumption. This is the 'puffed out' reading of the title.
Escape, weight, and what we skip
Escape speed is sqrt(2GM/R). It is the one-time ticket off the surface, not a daily commute. Your weight is still mg with the new g. What we skip: composition changes, a new day length, whether mountains can stand, whether the magnetic field survives. Those need a planetary-structure code. If you only wanted to feel heavier, the gravity-doubled experiment is a better fit. The dropdown here is the real experiment.
How we calculated this
Radius is Earth's mean radius times the multiple. Same-density mass is M⊕ × multiple³; same-mass mass is M⊕. Surface gravity = G × mass ÷ radius². Escape is sqrt(2GM/R). Weight uses the new g and the body-mass slider. Baseline constants from NASA Earth and NIST gn. Uniform-density ball; no core-mantle model.
Assumptions and limitations
This is a simplified estimate. Actual results depend on factors the model does not include.
This is a simplified thought experiment. It uses transparent assumptions so you can see what changes — it is not a full physical simulation of the real world.
- The planet is a sphere of uniform density in the same-density mode.
- Same-mass mode keeps M⊕ and only changes radius (density falls).
- Rotation, atmosphere and composition are not adjusted.
- Surface gravity ignores centrifugal relief.
- Escape speed is the frictionless, atmosphere-free figure.
Sources
- NASA Earth fact sheet
Mass, radius, rotation period and orbital speed used as the baseline Earth.
- NIST CODATA — standard acceleration of gravity
gn = 9.80665 m/s², the conventional standard gravity (also ISO 80000-3).
- NOAA NGS — WGS 84
Equatorial radius used for surface speed and centrifugal terms.
Go further
Related experiments that pick up where this one leaves off.
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