How big is Neptune compared to Mars?
Data as of July 2026
7.3×wider than Mars
Neptune is 7.3× wider than Mars: 49,244 km across against Mars’s 6,779 km. By volume, about 383 Marses would fit inside Neptune. Neptune has 160× Mars’s mass.
▶ See Neptune and Mars in 3D
Side by side
Diameter
Neptune 49,244 km · Mars 6,779 km
Width ratio
Neptune is 7.3× wider
Volume
383 Marses fit inside Neptune
Mass
Neptune is 160× Mars
Gravity (Neptune · Mars)
11.2 m/s² · 3.7 m/s²
Distance from Sun
30.1 AU · 1.52 AU
Neptune’s winds top 2,000 km/h, the fastest of any planet. The air on Mars is less than 1% as thick as Earth’s, so even its strongest winds push with very little force.
What sets them apart
Neptune is more than seven times wider than Mars and about 160 times its mass. Mars has been orbited, landed on and driven across for decades; Neptune has had a single visit, a flyby by Voyager 2 in 1989.
Ratios are easy to nod along to and impossible to picture. In the interactive view, switch to True scale to see Neptune and Mars at their honest relative sizes.
Keep going
✓ Facts verified July 2026
Every figure on this page is a real, rounded value checked against primary sources. Found something out of date? See how we keep it accurate.