[Cyberdemon]

The BMW gauge is very close to accurate. When I've had to run it very low I've put in 13 gallons when it said I had ~20 miles left on the meter.

I think this seems obvious, but compared to my old Acura - when that car said I had 0 miles remaining on the trip computer I still had about 2.5-3 gallons left in the tank.

My wife's jeep has a similar - extra idiot buffer. There is around 2 gallons left once the gauge reads zero.

TL;DR Americans and Asians are not as smart as Germans.

[FlyingScot1050]

The fuel gauge seems to be accurate, but the "distance to empty" calculation is annoyingly conservative

[Viffermike]

In my car with the extended gauges that come with the Tech Package, the low-warning system for fuel comes on in two steps that are based on miles to empty, NOT volume:

First warning: at 60 miles. Yellow warning text can be deactivated, though a small orange warning triangle remains as a reminder.
Second warning: at 30 miles. Red warning text comes back on after deactivation every couple of minutes, and a small red warning triangle replaces the yellow one as an always-on reminder.

Based on the tank capacity (13.7 gallons) and fill-ups when my tank has gotten as low as 5 miles left, there is no appreciable reserve built in to the warning system. I have not learned this the hard way, mind you, by actually running out of fuel -- and really the only way we'll know for absolute certain is if someone does run out of fuel and records the amount it takes to fill the tank.

But based on experience with past cars and what I state above, I don't bother with hope that there's a reserve. I fill the car up when it tells me to -- and switch to Eco Pro mode if I'm getting dangerously low (under 20 miles).

[Viffermike]

Originally Posted by FlyingScot1050

The fuel gauge seems to be accurate, but the "distance to empty" calculation is annoyingly conservative

That's because it varies based on a mix of short-term fuel consumption (within the last 10 minutes or so, I've found) and your average fuel consumption for the current tank. That's why the miles-to-empty figure will actually go up by several miles if you've done a lot of low-speed city driving, then get up onto a highway. The system gives you its best guess for how you are traveling and consuming at the time.

[B.a.f]

According to the manual and confirmed by what I have seen, there are two levels of warning.
The first happens when about 80 km are left and disappears after a few seconds. Then when only 50 km remain the autonomy displays permanently in the dashboard.