The Infinity-class is an attempt by Imperial Ship designers to make a scaled-back version of the Executor-class Super Star Destroyer. The Executor and Infinity classes are look so much alike that the Inifinity-class is blamed for much of the size confusion of the Executor. But, the Infinity is weak against starfighter attacks because its armament is designed for Capital Ship combat. It has to rely on Starfighter garrisons to protect it from Trench Runs.
its kinda small
In this picture it is. But in Star Wars, it would be about the size of 3 ISD's out in a line.