Question

What is the largest planet in the universe? In our galaxy? In our solar system? How do they compare in size?

Answer 1

Largest solar planet is Jupiter of size (diameter) 139822 km.
Largest in our galaxy Milky Way is supposedly HD100546 b of size about 7 times Jupiter's. No data now, for beyond Milky Way..

Explanation:

The exoplanet HD 199546 b, orbiting around the star HD 1000546 in

our galaxy Hilky Way, is supposed to be the largest known

exoplanet. It is 6.9 times as large as the largest planet Jupiter in our

solar system. This star is about 320 light years away.

Reference: wiki HD 1000546