Astronomy basics · Planet comparison
Planet Sizes in Order: Compared to Earth
The eight planets vary enormously in width. Compare their approximate equatorial diameters in kilometers and see each planet's diameter as a multiple of Earth's.
How big are the planets?
The table follows the planets outward from the Sun. Diameter means the width across a planet's equator, not its distance from the Sun or the volume of material it contains. Figures are rounded reference values from NASA's planetary data.
| Order | Planet | Diameter (km) | Earth diameters | Planet type |
|---|---|---|---|---|
| 1 | Mercury | 4,879 | 0.38× | Rocky |
| 2 | Venus | 12,104 | 0.95× | Rocky |
| 3 | Earth | 12,756 | 1.00× | Rocky |
| 4 | Mars | 6,792 | 0.53× | Rocky |
| 5 | Jupiter | 142,984 | 11.21× | Gas giant |
| 6 | Saturn | 120,536 | 9.45× | Gas giant |
| 7 | Uranus | 51,118 | 4.01× | Ice giant |
| 8 | Neptune | 49,528 | 3.88× | Ice giant |
Remember: Jupiter is the largest planet by diameter—about 11 times Earth's width. Mercury is the smallest. Venus is close to Earth in diameter, while Uranus and Neptune are each about four Earth diameters wide.
Why size comparisons can be surprising
Mercury, Venus, Earth, and Mars are rocky planets. Jupiter and Saturn are gas giants, while Uranus and Neptune are ice giants. Those groups differ in composition as well as size, so a planet's diameter alone does not tell you everything about what it is made of.
Diameter is also not the same as volume. If a planet is about 11 times wider than Earth, it has far more than 11 times Earth's volume. The comparison above is specifically about width across the equator.
Try a quick learning activity
- Predict which planet is largest before opening the model.
- Visit Mercury, Earth, Jupiter, and Neptune in Vastonaut's 3D explorer.
- Use the table to compare each one's diameter with Earth.
- Explain why the 3D scene is a navigation model and not a literal scale drawing of every planet and orbital distance.
Vastonaut compresses sizes and distances in parts of the interactive scene so worlds remain easy to find. Use published measurements for numerical comparisons rather than measuring pixels on the screen.
Scientific sources
- NASA Goddard Space Flight Center: Planetary Fact Sheet (Metric) — diameters and other planetary measurements.
- NASA Science: Planet Sizes and Locations in Our Solar System — planet size comparisons and order from the Sun.