Calculator
Enter known values, choose what to solve for, and the result will appear above this form.
Density comparison chart
The chart compares your result with several familiar planets using density in kg/m³.
Formula used
ρ = M / V
V = (4 / 3) × π × r³
ρ = M / ((4 / 3) × π × r³)
M = ρ × (4 / 3) × π × r³
r = ∛(3M / (4πρ))
Surface gravity: g = G × M / r²
Escape velocity: v = √(2GM / r)
This calculator assumes the object is roughly spherical. Real planets are layered and may be slightly flattened by rotation, so the result is best used as a global average density.
How to use this calculator
- Choose a preset planet for quick testing or keep custom mode.
- Select whether you want to solve for density, mass, or radius.
- Enter the known values using any supported unit combination.
- Click the calculate button to show results above the form.
- Review density, volume, gravity, escape velocity, and composition hints.
- Use the CSV or PDF buttons to save the current report.
- Check the chart to compare your result with reference planets.
Example data table
| Planet | Mass (Earth = 1) | Radius (Earth = 1) | Density (kg/m³) | Density (g/cm³) |
|---|---|---|---|---|
| Earth | 1.000 | 1.000 | 5514 | 5.514 |
| Mars | 0.107 | 0.532 | 3933 | 3.933 |
| Jupiter | 317.83 | 11.21 | 1326 | 1.326 |
| Saturn | 95.16 | 9.45 | 687 | 0.687 |
| Neptune | 17.15 | 3.88 | 1638 | 1.638 |
Values are rounded and intended for demonstration.
Frequently asked questions
1. What does planet density tell us?
Density shows how much mass is packed into a planet’s volume. Higher values usually suggest more rock and metal, while lower values often indicate more gas, ice, or a large low-density envelope.
2. Why is radius so important in density calculations?
Volume depends on radius cubed. That means a modest radius error can create a much larger density error. Reliable radius measurements are essential when comparing planets or studying exoplanet composition.
3. Can I use Earth masses and Earth radii together?
Yes. The calculator converts all supported units into base SI values before calculating. Mixing Earth-based and Jupiter-based units is fine as long as each input is paired with the correct unit selector.
4. Is this result an average density?
Yes. The result is a bulk or average density for the whole planet. It does not show internal layers separately, so a planet with a dense core and light atmosphere still gets one combined value.
5. Can this calculator help identify rocky or gaseous worlds?
It can provide a useful clue. Dense planets are often rocky or metal-rich, while low-density planets are commonly gas-rich. Composition still needs more evidence, including atmosphere, temperature, and stellar data.
6. Why are gravity and escape velocity included?
They add physical context to the density result. Surface gravity helps compare weight conditions, and escape velocity helps describe how strongly the planet holds gas and other material near it.
7. Can I reverse solve for mass or radius?
Yes. Choose the solve mode first. The calculator can determine density from mass and radius, mass from density and radius, or radius from mass and density using the spherical planet equations.
8. Does this work for exoplanets too?
Yes, as long as you have reasonable estimates for mass, radius, or density. The method is the same, but exoplanet measurements often have larger uncertainty than values for planets in our solar system.