One point to keep in mind is that when you fill up to the first click ... your tank is not necessarily completely full. i.e if your tank capacity is 12.3 gallons ... there is no guarantee that at first click your tank is holding the full 12.3 gallons. I don't know the full details but it has something to do with the vapor / pressure thingy means.

So I'd rather not assume that there's still 2 gallons left when the last bar goes off. Obviously I belong to the "better safe than sorry" tribe .

 

In fact, it's certainly *not* full at first click-off. The standard thinking seems to be between 1.8 and 2.0 gallons from first click-off to full-up-the-neck. Now, obviously, there's a difference between tank-full and neck-full, but no way is it 1.8 gallons difference. So, probably there's a gallon or so left to fill the tank itself after first click-off.

Still, the gas gauge doesn't care how full your tank was to begin with when it displays no bars. For your own car, you can carefully establish a reliable sense of how many gallons (or fractions thereof) are left at no bars just by paying attention to how far you're driving beyond no bars at what mileage, or by comparing a known fill (X number of gallons) to how many bars show, a few different times.

--doug