Mars has a diameter of approximately 6,779 to 6,794 kilometers (about 4,212 to 4,222 miles), which is a little more than half (about 53%) the diameter of Earth

. Its equatorial diameter is about 6,794 km, while the pole-to-pole diameter is slightly smaller at about 6,752 km, making Mars an oblate spheroid rather than a perfect sphere

. The radius of Mars is roughly 3,390 kilometers (2,106 miles)

. In summary:

• Diameter: ~6,779–6,794 km (4,212–4,222 miles)
• Radius: ~3,390 km (2,106 miles)
• About half the size of Earth in diameter (53% of Earth's diameter)

This size makes Mars the second smallest planet in the solar system after Mercury