General Requirements:
Hungary tourist visa is not required for citizens of United States for a stay up to 90 days. The passport should be valid for at least three months beyond the periods of stay. However, it is strongly recommended traveling with 6 months validity on your passport at all times.
Most destinations, including Hungary, require that you have adequate un-used pages in your passport, allowing for any necessary stamps upon arrival and departure. It is recommended that you have at least two free pages in Visas section of your passport before any international travel. U.S. citizens can get extra passport pages added to their passports as fast as within 24 hours.
General Consulates of Hungary: