Twice the source mean radius; body diameter only, excluding rings.
Earth is our anchor for understanding the unfamiliar. Start here, then put Jupiter or the Sun beside it. The circle that holds every everyday journey quickly becomes a small detail in the scene.
How big is Earth?
The value here is a volume-equivalent mean diameter: the diameter of a sphere with the same volume. Earth is not a perfect sphere, so an equatorial diameter produces a slightly different comparison.
Turn Earth into something you can hold
Set Earth as the first object and leave the marble at 2 cm. The other object is scaled down by exactly the same factor. Try the Earth and Jupiter comparison to begin.