How big is Neptune compared to Mercury?
Data as of July 2026
10.1×wider than Mercury
Neptune is 10.1× wider than Mercury: 49,244 km across against Mercury’s 4,879 km. By volume, about 1,028 Mercuries would fit inside Neptune. Neptune has 311× Mercury’s mass.
▶ See Neptune and Mercury in 3D
Side by side
Diameter
Neptune 49,244 km · Mercury 4,879 km
Width ratio
Neptune is 10.1× wider
Volume
1,028 Mercuries fit inside Neptune
Mass
Neptune is 311× Mercury
Gravity (Neptune · Mercury)
11.2 m/s² · 3.7 m/s²
Distance from Sun
30.1 AU · 0.39 AU
In one Neptune year, about 165 Earth years, Mercury goes round the Sun about 680 times.
What sets them apart
The outermost planet against the innermost. Neptune is about ten times wider than Mercury and some 310 times its mass, and it orbits about 77 times farther from the Sun.
Ratios are easy to nod along to and impossible to picture. In the interactive view, switch to True scale to see Neptune and Mercury 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 Found something out of date?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.