Knowing fighter squadron sizes is useful for new scenario builders.
Though not perfect in every single case, a good rule of thumb for a fighter squadron deployed at an air base in Command is 10-24 aircraft. The low-end is for an underequipped or battered unit, the high-end is for a USAF squadron at full paper strength. (In the middle are US Navy carrier squadrons at 11-15 and OPFOR squadrons at 12-16).
A substantial portion of the squadron will be down for maintenance at any time in even the best-case scenarios, so set a few to “maintenance-unavailable”.