You’re probably thinking of surface gravity: The Moon’s surface gravity is about 1/6 that of Earth. While gravity does depend on the object’s mass, it also depends on distance, and since the Moon has a smaller radius, you’re closer to its center when you stand on its surface. A spherical object’s surface gravity works out to be proportional to its diameter times its density, so the fact that the diameter-fraction is relatively close to the surface-gravity-fraction is not a coincidence: It just means that the Earth and the Moon are close to the same density, but the Earth is a little denser.
Thanks, I think that’s it exactly. I remember learning as a kid that your weight on the moon is 1/6 your weight on the earth, which I somehow turned into 1/4. And then knowing that gravity depends on mass, I guess I figured the moon was 1/6 (1/4) the mass of the earth…and somewhere along the line, mass became volume (I guess I assumed the densities were the same).
Sounds like a stupid logical progression now, but I’m sure it made sense as a kid, and then it just got ingrained in my melon - hence my surprise at the picture.