Mercury
Small world. Big extremes.
How big is Mercury? Mercury is 4,879 km (3,032 miles) across at its equator — 0.38 times Earth’s width (about 38%) — and about 17.8 Mercury-sized worlds would fit inside Earth. Gravity at the surface is 3.7 m/s², 0.38 times Earth’s.
A cratered, rocky world with almost no atmosphere to carry heat from day to night. Mercury races around the Sun while turning slowly on its axis.
Image: NASA / Johns Hopkins University Applied Physics Laboratory / Carnegie Institution of Washington. Processed mission imagery; apparent color varies with filters and processing.
Mercury quick facts
| Planet type | Terrestrial planet |
|---|---|
| Equatorial diameter | 4,879 km (3,032 mi) |
| Mean radius | 2,439.7 km (1,516 mi) |
| Size compared with Earth | 0.38× as wide · 0.056× the volume |
| Equatorial circumference | 15,328 km (9,524 mi) |
| Surface area | 7.48 × 10⁷ km² |
| Volume | 6.08 × 10¹⁰ km³ |
| Mass | 3.30 × 10²³ kg (0.055 Earth masses) |
| Mean density | 5,429 kg/m³ (5.43 g/cm³) |
| Surface gravity | 3.7 m/s² (0.38× Earth) |
| Escape velocity | 4.3 km/s |
| Length of day (solar) | 175.9 Earth days (4,222.6 hours) |
| Rotation period (sidereal) | 58.7 Earth days |
| Orbital period (year) | 88 Earth days (0.24 Earth years) |
| Mean distance from the Sun | 57.9 million km (36 million mi) · 0.39 AU |
| Closest and farthest from the Sun | 46 – 69.8 million km |
| Distance from Earth | 77.3 – 221.9 million km |
| Sunlight travel time | 3.2 minutes |
| Mean orbital speed | 47.4 km/s |
| Axial tilt | 0.034° |
| Mean temperature | 167 °C |
| Known moons | 0 |
| Ring system | No |
Reference: NASA Planetary Fact Sheet. Rounded values; diameters are equatorial, area and volume use the mean radius. Moon counts include discoveries announced through 2025 (such as Uranus’s S/2025 U1) and keep growing as new moons are confirmed.
How big is Mercury compared to Earth?
Mercury’s equatorial diameter of 4,879 km makes it 0.38 times Earth’s width (about 38%). By volume, about 17.8 Mercury-sized worlds would fit inside Earth. Its mass is 0.055 times Earth’s, so its average density is similar: 5,429 kg/m³ (5.43 g/cm³).
Earth’s equatorial diameter is 12,756 km (7,926 miles). See every planet to scale ↗
What is the gravity on Mercury?
Gravity on Mercury is about 3.7 m/s² at the surface: 0.38 times Earth’s 9.8 m/s². Someone who weighs 100 lb on Earth would weigh about 38 lb on Mercury. To escape its pull, a rocket needs 4.3 km/s.
Calculate your weight on Mercury ↗How far is Mercury from the Sun and Earth?
Mercury orbits an average 57.9 million km (36 million miles, 0.39 AU) from the Sun, ranging from 46 to 69.8 million km. Sunlight takes 3.2 minutes to get there. Its distance from Earth varies from about 77.3 to 221.9 million km.
Time sunlight’s journey ↗How long is a day and a year on Mercury?
A solar day on Mercury lasts 175.9 Earth days (4,222.6 hours), and one spin relative to the stars takes 58.7 Earth days. A year — one trip around the Sun at 47.4 km/s — lasts 88 Earth days (0.24 Earth years). Its axis is tilted 0.034°.
Watch the orbit ↗Is Mercury a rocky planet or a gas giant?
No. Mercury is a terrestrial, or rocky, planet with a solid surface of rock and metal — one of the four inner planets with Mercury, Venus, Earth and Mars. The gas giants are Jupiter and Saturn.
Meet all eight planets ↗Mercury questions, answered
How big is Mercury compared to Earth?
Mercury is 4,879 km (3,032 miles) wide at its equator, 0.38 times Earth’s width (about 38%). By volume, about 17.8 Mercury-sized worlds would fit inside Earth, and its mass is 0.055 times Earth’s.
What is the gravity on Mercury?
Gravity on Mercury is about 3.7 m/s² at the surface, or 0.38 times Earth’s. Someone who weighs 100 lb on Earth would weigh about 38 lb there; escape velocity is 4.3 km/s.
What is the mass of Mercury?
Mercury has a mass of about 3.30 × 10²³ kg, or 0.055 Earth masses. Its mean density is 5,429 kg/m³ (5.43 g/cm³).
How far is Mercury from Earth?
The distance changes as both planets orbit the Sun. Mercury comes within about 77.3 million km of Earth and can be as far as 221.9 million km away. It orbits 0.39 AU from the Sun on average.
How long is a year on Mercury?
One orbit takes about 88 Earth days (0.24 Earth years). A solar day on Mercury lasts 175.9 Earth days (4,222.6 hours).
Is Mercury a rocky planet or a gas giant?
No. Mercury is a terrestrial, or rocky, planet with a solid surface of rock and metal — one of the four inner planets with Mercury, Venus, Earth and Mars. The gas giants are Jupiter and Saturn.
What is the density of Mercury?
Mercury’s mean density is 5,429 kg/m³ (5.43 g/cm³). Earth’s is 5,514 kg/m³.