How much would a 100 pound person weigh on Neptune?

A 100-pound person who stood, or floated, on the surface of Neptune would weigh 114 pounds. Although Neptune is much more massive than Earth, it's far less dense, so the acceleration of gravity at its surface is weaker than expected for a planet that is 17 times Earth's mass.

Neptune is a gas giant, and it lacks the solid surface of rocky planets such as Earth. Neptune's "surface" is defined as the point at which its atmosphere exerts 15 pounds of pressure per square inch, which is equal to sea level on Earth. At this point on Neptune, the distance from the planet's center of mass is so great that the force of gravity is only 114 percent of that felt on the much more dense Earth.