How long do I have to stay outside of the Schengen Area? [duplicate]

You must stay out for 90 days, as you're allowed to stay for 90 days in a 180-day period.

Bear in mind, if you do find yourself a job and decide to move there, for most countries you'll have to go back home and apply for a Long-stay visa, then re-enter and obtain a residence permit. However, Germany, for example, does let Americans apply for a residence permit during a visa-free visit.

You must use so called 90/180 rule: 90 days within 180 days, so if you've stayed the full 90 days in the Schengen zone, you must wait for 90 days before you are allowed to re-enter the Schengen zone visa free.