Which is the biggest planet?
Jupiter. Its radius is 69,911 km, 11.0 times Earth’s, and it is 318 times as massive as Earth.
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The planets compared: size, gravity, day and year
Jupiter is the biggest planet and has the strongest gravity; Mercury is the smallest; Venus has the longest day; Saturn is the only planet less dense than water. Averaged over time, Mercury — not Venus — is Earth’s nearest neighbour.
| Planet | Radius (Earth = 1) | Mass (Earth = 1) | Gravity (g) | Density (g/cm³) | Day (rotation) | Year | From the Sun (mean) | Average from Earth* |
|---|---|---|---|---|---|---|---|---|
| Mercury | 0.383 | 0.055 | 0.38 | 5.43 | 58.65 days | 87.97 days | 0.387 AU | 1.04 AU |
| Venus | 0.950 | 0.815 | 0.90 | 5.24 | 243.02 days ↺ | 224.70 days | 0.723 AU | 1.14 AU |
| Earth | 1.000 | 1.0 | 1.00 | 5.51 | 23.9 hours | 365.26 days | 1.000 AU | — |
| Mars | 0.532 | 0.107 | 0.38 | 3.93 | 24.6 hours | 1.88 years (687 days) | 1.524 AU | 1.70 AU |
| Jupiter | 10.973 | 317.8 | 2.64 | 1.33 | 9.9 hours | 11.86 years (4,333 days) | 5.203 AU | 5.27 AU |
| Saturn | 9.140 | 95.2 | 1.14 | 0.69 | 10.7 hours | 29.46 years (10,759 days) | 9.537 AU | 9.58 AU |
| Uranus | 3.981 | 14.5 | 0.92 | 1.27 | 17.2 hours ↺ | 84.02 years (30,689 days) | 19.189 AU | 18.70 AU |
| Neptune | 3.865 | 17.1 | 1.15 | 1.64 | 16.0 hours | 164.77 years (60,182 days) | 30.070 AU | 29.82 AU |
* Our own calculation: distance from Earth averaged every 2 days over 2026–2056 using NASA JPL Horizons orbits. ↺ = rotates backwards. Radius and mass from JPL; gravity at the surface or 1-bar cloud level.
Frequently asked questions
Which is the smallest planet?
Mercury, with a radius of 2,440 km — only 38% of Earth’s and smaller than Jupiter’s moon Ganymede.
Which planet has the strongest gravity?
Jupiter: 2.64 times Earth’s gravity at the cloud tops. Saturn, despite its size, has only 1.14 g.
Which planet has the longest day?
Venus. It turns once every 243 Earth days — longer than its 225-day year — and it spins backwards.
Which planet is closest to Earth?
It depends what you mean. Venus comes closest (about 38 million km). But averaged over time, Mercury is the nearest planet to Earth: 1.038 AU (155.3 million km) on average over 2026–2056 in our calculation, because it never strays far from the Sun.
Which planet is the least dense?
Saturn, at 0.69 g/cm³ — less than water (1.00 g/cm³). Earth is the densest planet at 5.51 g/cm³.