Mercury
Mercury is a rocky planet orbiting closest to the Sun in the Solar System.
How big is it?
4,879 km · mean diameter
Mean diameter · approximate
A little perspective
Mercury vs Callisto: diameter comparison
The mean diameter of Mercury is about 1.01 times the mean diameter of Callisto.
Mercury is a rocky planet orbiting closest to the Sun in the Solar System.
Callisto is a natural satellite of Jupiter, with a heavily cratered icy surface.
Both rulers start at the same zero and share one linear scale. Artwork keeps its original proportions.
Measurements, assumptions & sources +
Mercury
Mean diameter: 4,879 km; approximate.
Mean-radius spherical model for Mercury; actual shape is not perfectly spherical.
NASA JPL — planetary physical parameters
The marked mean diameter is calibrated. Unmeasured illustration details are representative.
Callisto
Mean diameter: 4,821 km; approximate.
Rounded mean-radius model of Callisto. 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 4,879 km
We compare the mean diameter of Mercury. This is an estimate; check the notes for its rounding and uncertainty.
Mean-radius spherical model for Mercury; actual shape is not perfectly spherical.
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 |
|---|---|---|---|
| 4,879 km | Not recorded | approximate | |
| 2,439 km | Not recorded | approximate | |
| 15,330 km | Not recorded | derived | |
| 74,780,000 km² | Not recorded | derived | |
| 6.08 × 10¹⁰ km³ | Not recorded | derived | |
| 3.301 × 10²⁰ t | Not recorded | approximate | |
| 3.7 m/s² | Not recorded | approximate | |
| 0.3871 AU | Not recorded | rounded orbital anchor | |
| 170,500 km/h | Not recorded | rounded orbital anchor |
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 spaceCallisto4,821 kmMean diameterCallisto is a natural satellite of Jupiter, with a heavily cratered icy surface.
Nearest higher valuePlanets, moons and spaceTitan5,150 kmMean diameterTitan is a natural satellite of Saturn, with a thick nitrogen-rich atmosphere and surface lakes of hydrocarbons.Sources and method
Want to check the number?
The source records and measurement method remain available for inspection.
- NASA JPL — planetary physical parametersMean radii and masses. Spherical area and volume here are derived from mean radius. This atlas rounds for scale comparison.
- NASA — Planet CompareConventional surface gravities; giant-planet values refer to an atmospheric reference level. Earth uses standard gravity, 9.80665 m/s².
- Defined examples — our methodology
More ways to see it
Curated comparisons
There’s always another scale
Follow your curiosity.
SpaceEarth12,740 kmEarth is the rocky planet on which we live and the third planet from the Sun.SpaceMoon3,475 kmThe Moon is Earth’s natural satellite and the brightest large object in Earth’s night sky.
SpaceJupiter139,800 kmJupiter is a giant planet composed mainly of hydrogen and helium, orbiting the Sun beyond the asteroid belt.
SpaceSun1,391,000 kmThe Sun is the star at the centre of the Solar System.SpaceCallisto4,821 kmCallisto is a natural satellite of Jupiter, with a heavily cratered icy surface.SpaceTitan5,150 kmTitan is a natural satellite of Saturn, with a thick nitrogen-rich atmosphere and surface lakes of hydrocarbons.
SpaceGanymede5,262 kmGanymede is a natural satellite of Jupiter and contains a magnetic field generated by its partially liquid core.
SpaceIo3,643 kmIo is a natural satellite of Jupiter, covered with active volcanoes and sulphur deposits.