Whenever I fill up, I manage to go about 100 miles before the first pip falls. Then the next two fall pretty quickly, and then after that the decline takes place fairly evenly. I am averaging about 54 mpg and fill up every 450 miles or so, when there's just one or two pips left. I remember with my year-2000 Camry, the gas meter would fall very slowly for the first quarter tank, then fall pretty rapidly until the last quarter. When it hit the 1/4 tank reading, there would only be 3 gallons in the tank, even though I had a 16-gallon tank. I guess some Toyota models just have their own quirks when it comes to the fuel gauge.
I was a bit concerned yesterday afternoon when the last pip started flashing on me. The distance to empty was down to 18 miles. The station was packed so I waited until this morning to fill up. I had to break my own rule never to get gas when the supply truck is filling the underground tanks but I felt I had no choice. The next closest station is 10 hilly miles down the road. To my surprise, the tank only took 8.5 gallons to the autoshutoff. I can understand a bit of "error on the safe side" but 3 gallons is 1/4 tank. Is running out of gas in a Prius really that serious?