How much fuel is filled in airplane?

Answer 1

At least enough to reach your first destination, plus a reserve - small planes flying under visual flight rules can carry 30 minutes reserve fuel, everyone else needs to carry 45 minutes reserve fuel.

Answer 2

That depends entirely on what airplane. It can be as little as 40 gallons on small civil aircraft to as much as 6,000 gallons on some large airliners.