Was checking some details and put together this reference. I'm sure they'll be a deference in scale for spacecraft but it does give you a starting point.
Relative combat ship size by length:
Aircraft Carrier - 800-1100 feet
Battleship - 800-900 feet
Heavy Cruiser - approx. 700 feet
Light Cruiser - approx. 600 feet
Destroyer - approx. 550 feet
Guided Missile Destroyer - approx. 500 feet
Frigate - typically 400-450 feet
Patrol boats, Corvettes and Littoral Combat Ships - typically around 300-420 feet
Note: Ship designations are also relative to armament and purpose, and not size alone.