Io
Io is a natural satellite of Jupiter, covered with active volcanoes and sulphur deposits.
How big is it?
3,643 km · mean diameter
Mean diameter · approximate
A little perspective
Io vs Moon: diameter comparison
The mean diameter of Io is about 1.05 times the mean diameter of the Moon.
Io is a natural satellite of Jupiter, covered with active volcanoes and sulphur deposits.
The Moon is Earth’s natural satellite and the brightest large object in Earth’s night sky.
Both rulers start at the same zero and share one linear scale. Artwork keeps its original proportions.
Measurements, assumptions & sources +
Io
Mean diameter: 3,643 km; approximate.
Rounded mean-radius model of Io. The derived area and volume describe a sphere; surface terrain and flattening are omitted.
NASA JPL — Planetary satellite physical parameters
The marked mean diameter is calibrated. Unmeasured illustration details are representative.
Moon
Mean diameter: 3,475 km; approximate.
Rounded mean-radius model of Moon. The derived area and volume describe a sphere; surface terrain and flattening are omitted.
NASA JPL — Planetary satellite physical parameters
The marked mean diameter is calibrated. Unmeasured illustration details are representative.
Use the visual comparison to explore its scale, then check the measurements and sources.
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Why this measurement?
Why we use 3,643 km
We compare the mean diameter of Io. This is an estimate; check the notes for its rounding and uncertainty.
Rounded mean-radius model of Io. The derived area and volume describe a sphere; surface terrain and flattening are omitted.
The marked horizontal span follows the measured feature, not the edges of the image. How calibrated comparisons work →
Recorded properties
Dimensions and measurements
| Property | Selected value | Recorded range | Basis |
|---|---|---|---|
| 3,643 km | Not recorded | approximate | |
| 41,690,000 km² | Not recorded | derived | |
| 2.531 × 10¹⁰ km³ | Not recorded | derived | |
| 8.93 × 10¹⁹ t | Not recorded | derived | |
| 1.796 m/s² | Not recorded | derived |
Around this scale
Explore nearby values.
Compare examples with lower, similar and higher values. Each card names the measurement being compared.
Nearest lower valuePlanets, moons and spaceMoon3,475 kmMean diameterThe Moon is Earth’s natural satellite and the brightest large object in Earth’s night sky.
Around the same scalePlanets, moons and spacePluto2,377 kmMean diameterPluto is a dwarf planet in the Kuiper Belt, composed of rock and ice and orbiting the Sun.
Nearest higher valuePlanets, moons and spaceCallisto4,821 kmMean diameterCallisto is a natural satellite of Jupiter, with a heavily cratered icy surface.Sources and method
Want to check the number?
The source records and measurement method remain available for inspection.
- NASA JPL — Planetary satellite physical parametersPublished mean radii and gravitational parameters GM. Spherical areas, volumes, masses and local gravity are explicitly derived.
More ways to see it
Curated comparisons
There’s always another scale
Follow your curiosity.
SpaceMoon3,475 kmThe Moon is Earth’s natural satellite and the brightest large object in Earth’s night sky.
SpaceEarth12,740 kmEarth is the rocky planet on which we live and the third planet from the Sun.SpacePluto2,377 kmPluto is a dwarf planet in the Kuiper Belt, composed of rock and ice and orbiting the Sun.
SpaceJupiter139,800 kmJupiter is a giant planet composed mainly of hydrogen and helium, orbiting the Sun beyond the asteroid belt.
SpaceEuropa3,122 kmEuropa is a natural satellite of Jupiter, with a smooth icy surface thought to cover a subsurface ocean.SpaceCallisto4,821 kmCallisto is a natural satellite of Jupiter, with a heavily cratered icy surface.
SpaceMercury4,879 kmMercury is a rocky planet orbiting closest to the Sun in the Solar System.
SpaceTriton2,705 kmTriton is a natural satellite of Neptune, with a retrograde orbit and a surface of frozen nitrogen.