How big is Neptune compared to Earth?
3.9×wider than Earth
Neptune is 3.9× wider than Earth — 49,244 km across against Earth’s 12,742 km. By volume, about 58 Earths would fit inside Neptune. It has 17.1× Earth’s mass, and its cloud-top gravity is 1.14× Earth’s.
▶ See Neptune next to Earth in 3D
Side by side
Width vs Earth
3.9× wider
Volume vs Earth
58 Earths fit inside
Mass vs Earth
17.1× Earth’s mass
Cloud-top gravity
1.14× Earth (11.2 m/s²)
You’d weigh
80 kg at the cloud tops (if 70 kg here)
Diameter
49,244 km
Line up 4 Earths side by side and they’d just span Neptune’s width — but volume grows with the cube of width, so it takes about 58 Earths to actually fill it.
What that actually feels like
Neptune was found in 1846 exactly where mathematicians said an unseen planet must be, from the way it tugged on Uranus — the first world discovered by prediction rather than accident. It has completed just one orbit of the Sun since. How the dimmest, coldest planet powers the fastest winds in the solar system is still not fully understood.
Ratios on a page are easy to nod along to and impossible to picture. In the interactive view, switch to True scale to see Neptune and Earth at their honest relative sizes — the gap is even more startling than the numbers suggest.
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 Found something out of date?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.