They're pretty inaccurate in light aircraft where you're often flying at an angle / slightly asymmetrically; in commercial airliners, under most flight conditio

They're pretty inaccurate in light aircraft where you're often flying at an angle / slightly asymmetrically; in commercial airliners, under most flight conditions, they're generally within a couple percent. Aircraft will generally use fuel flow sensors and use those to calculate remaining fuel (by integrating the fuel flow over time) and float/capacitance sensors in tanks are used as verification / a sanity check (which can sometimes only end up being noticed inflight, eg https://www.flightglobal.com/safety/boeing-modifying-777-fuel-indicator-after-in-flight-discrepancy-incidents/138706.article https://www.flightglobal.com/safety/boeing-modifying-777-fue...) For more than you'd ever want to know about the fuel systems in a modern airliner, see http://www.b737.org.uk/fuel.htm http://www.b737.org.uk/fuel.htm