In aviation, why is altitude always measured in feet?

Why? Because the Americans felt comfortable with that, and the rest of the world followed! read more

The answer to"why" is standardization. Feet was probably chosen as a result of the rapid growth of airline travel led by the US after WW II. There are two major areas in the world where altitude is measured in meters: China and Russia (there might be a couple more). read more

Anyway, the ICAO Annex 5 specifies units to use, including units for altitude and actually specifying meters as the primary unit, with feet being accepted as non-SI alternative. Why on earth you'd want to go against the majority on this I don't know, perhaps due to the fact that it's an SI unit and they want to be as much SI as they can. read more

Pressure altitude divided by 100 feet (30 m) is the flight level, and is used above the transition altitude (18,000 feet (5,500 m) in the US, but may be as low as 3,000 feet (910 m) in other jurisdictions); so when the altimeter reads 18,000 ft on the standard pressure setting the aircraft is said to be at"Flight level 180". read more