Planet Density Calculator

• Density: ρ = m / V
• Sphere volume: V = (4/3) · π · r³
• Unit link: 1 g/cm³ = 1000 kg/m³

1. Select a method that matches your known measurements.
2. Enter mass, plus either radius/diameter or volume.
3. Use unit menus to match your source data.
4. Press Calculate to view results above the form.
5. Download CSV for spreadsheets or PDF for sharing.

Planet Density Guide

1) Why density matters in planetary science

Density links what you can observe to what a planet is made of. A world with high density usually contains more rock and metal, while a low-density world may be rich in ice, gas, or have a puffier atmosphere.

2) Mean density versus interior layers

This tool returns a mean density, averaged across the entire planet. Earth averages about 5.51 g/cm³, yet its core is much denser than its crust. Mean density is still powerful for first-pass composition checks.

3) The calculator’s core relationship

The central idea is simple: ρ = m / V. When you supply radius or diameter, the calculator uses the spherical volume V = 4/3·π·r³. If you already know volume, you can compute density directly.

4) Input methods and when to use them

Mass + Radius fits most planets with measured size and mass. Mass + Volume helps irregular bodies when volume is independently estimated. Radius + Density lets you estimate mass when a plausible density is known.

5) Units and quick conversions

Use kg, Earth masses, or Jupiter masses for mass, and km or Earth radii for size. The calculator also converts between kg/m³ and g/cm³. Remember: 1 g/cm³ = 1000 kg/m³.

6) Interpreting typical density ranges

Rocky planets often fall near 3–8 g/cm³ depending on iron content. Icy bodies can be around 1–3 g/cm³. Gas giants are frequently near 0.7–1.7 g/cm³, despite enormous mass, because their volumes are huge.

7) Example comparison using familiar worlds

Earth (~5.51 g/cm³) and Venus (~5.24 g/cm³) suggest rock-metal interiors. Mars (~3.93 g/cm³) indicates lower average metal fraction. Jupiter (~1.33 g/cm³) and Neptune (~1.64 g/cm³) reflect thick envelopes of hydrogen, helium, and ices.

8) Accuracy tips and common pitfalls

Small radius errors strongly affect volume because volume scales with r³. Keep units consistent, prefer mean radius values, and treat “sphere” results as approximations for oblate or irregular bodies. For exoplanets, uncertainties can be large, so interpret density as a range.

FAQs

1) What is “mean density”?

Mean density is total mass divided by total volume. It summarizes a planet as one average number, even though real planets have layered interiors with different densities.

2) Why does radius matter so much?

When volume is derived from radius, volume scales as r³. A small radius change can produce a much larger volume change, which then alters density significantly.

3) Should I use radius or diameter?

Either works. If you enter diameter, the calculator converts it to radius internally. If both are entered, diameter is used only when radius is empty.

4) How do I switch between kg/m³ and g/cm³?

The results section shows both. The conversion is fixed: 1 g/cm³ equals 1000 kg/m³. This is useful when comparing with geology or materials data.

5) Can I use Earth or Jupiter units?

Yes. Mass can be entered in Earth, Jupiter, or Solar masses, and size can be entered in Earth or Jupiter radii. The calculator converts everything to SI before computing density.

6) What if the planet is not perfectly spherical?

This calculator assumes a sphere when converting radius to volume. For oblate planets or irregular bodies, prefer a measured volume method or treat the density as an approximation.

7) Can I estimate mass from density and radius?

Yes. Choose the “Radius + Density → Mass” method. Provide a realistic density and a radius or diameter, and the calculator will compute mass from density times volume.