Flight hours

Flight hours is an aviation term referring to the total amount of time spent piloting aircraft, and serves as the primary measure of a pilot's experience. Flight hours (or flight time) is defined as "when an aircraft moves under its own power for the purpose of flight and ends when the aircraft comes to rest after landing." Time spent taxiing and performing pre-flight checks on the ground is included in flight hours, provided the engine is running.
Recording flight time.
Most government licensing regulations have specific flight hour requirements, as do virtually all airline job listings. Consequently, all pilots maintain a logbook (at least while pursuing a license or to record proof of recurrent training). A pilot's logbook is considered a legal document. Most pilots maintain a traditional hard copy, but electronic versions such as the one included with the popular app "ForeFlight" are allowed. Flight hours are recorded in 0.1 hour increments, which correspond to the resolution of a typical Hobbs meter, an odometer-like instrument installed in most cockpits. Pilots record many details about their flight time, such as whether a flight occurred during the day or at night, in a single- or multi-engine aircraft, in visual or instrument conditions, and the pilot's role during the flight.
Required hours by certificate/rating.
Pilots are required to accumulate a certain number and type of flight hours for each certificate or rating. The requirements become more numerous with each successive rating, but most requirements can be "stacked" (i.e. flying cross-country in instrument conditions fulfills both cross-country and instrument hour requirements). Detailed requirements for each rating can be found in 14 CFR Part 61 and in the sections to follow.
Overview.
While it is theoretically possible to achieve a certificate/rating at the minimum hour requirements, pilots are required to demonstrate proficiency before they can take the written, oral, and practical tests for each. The Private Pilot Certificate in particular is known to take students more than the legal minimum hours to complete. These minimums were set decades ago, before the era of complex GPS units and an increasingly regulated National Airspace System. The national average for the Private Pilot Certificate is currently estimated at 60-75 hours.
Private Pilot Certificate.
According to FAR Part 61.109(a), to be eligible for a Private Pilot Certificate the following aeronautical experience requirements must be met:
Instrument Rating.
According to FAR Part 61.65(d), to be eligible for an Instrument Rating the following aeronautical experience requirements must be met:
Commercial Pilot Certificate.
According to FAR Part 61.129(a), to be eligible for a Commercial Pilot Certificate the following aeronautical experience requirements must be met:
Private Pilot Certificate, Multi-Engine Rating.
According to FAR Part 61.109(a), to be eligible for a Multi-Engine Rating the following aeronautical experience requirements must be met:
Commercial Pilot Certificate, Multi-engine Rating.
According to FAR Part 61.129(a), to be eligible for a Commercial Pilot Certificate, Multi-Engine Rating the following aeronautical experience requirements must be met:
Air Transport Pilot Certificate.
According to FAR Part 61.159(a), to be eligible for an Air Transport Pilot Certificate the following aeronautical experience requirements must be met: