Earth Similarity Index calculator
Score any planet's similarity to Earth on a 0 to 1 scale, where Earth is 1.0. Enter a radius and a temperature, add density and mass if you know them, and read off the ESI: the same published formula gravityfinder computes for every known world.
This world would be strikingly Earth-like in size and warmth. Scored on radius, temperature, density, escape velocity (from mass and radius).
| Property | Earth reference | Weight |
|---|---|---|
| Radius (required) | 1 Earth radius | 0.57 |
| Equilibrium temperature (required) | 255 kelvin | 5.58 |
| Bulk density (when known) | 5.51 g/cm³ | 1.07 |
| Escape velocity (when known) | Earth's (from mass and radius) | 0.70 |
Each property is compared with Earth's reference value, raised to its weight, and the terms are combined as a geometric mean. Temperature carries by far the most weight, which is why a scorched or frozen world scores low no matter how Earth-sized it is.
How do you calculate the Earth Similarity Index?
The Earth Similarity Index is the geometric mean of similarity terms for radius, equilibrium temperature, and, where known, bulk density and escape velocity (the Schulze-Makuch 2011 weighting). Each term compares the planet's value with Earth's reference value on a 0 to 1 scale, so Earth's own numbers score exactly 1.0.
What inputs does the ESI calculator need?
Radius (in Earth radii) and equilibrium temperature (in kelvin) are required. Density (in grams per cubic centimeter) and mass (in Earth masses) are optional: when you supply them, the score also weighs density and escape velocity, which is what keeps dense super-Earths honest.
Why does Earth score exactly 1.0?
Every term in the index compares a planet's value with Earth's reference value, so Earth's own inputs (1 Earth radius, the 255 kelvin equilibrium basis, 5.51 g/cm³, 1 Earth mass) score 1.0 by construction. The 255 kelvin figure is Earth's equilibrium temperature: the balance point from sunlight alone, before greenhouse warming lifts the real surface average.
Where can I see real planets' ESI values?
gravityfinder computes the Earth Similarity Index for every confirmed exoplanet with a measured size and temperature, and ranks them all: the leaderboard lists the top 100, and each ranked world's planet page shows its score and rank.
Keep exploring: every world ranked by ESI · what the index means · the most Earth-like record
Uses the published Schulze-Makuch 2011 formula. Earth Similarity Index computed by gravityfinder, independently of any third-party habitability catalog.