Just based on my personal experience, where each time that I have filled up (with 6850 miles on my Prius V) I have added approximately 10 gallons. Since there are 10 'pips' on the fuel display, I have used that to indicate that there is approximately 1 gallon per pip. That said, I know that sometimes I will drive over 150 miles before the first pip drops, and that I have seen the last two pips go in 50 miles, so it varies. There are other posts here that mention that, do a searh to find them.
I'm with stupid (hehe). I'm using the 1 pip per gallon technique too. I'd also look at how many miles it calculates till empty and divide that by what you normally average per gallon. I say this because the other day I drove it till the 2nd pip turned to 1 and I had about 40-50 miles left till empty, which coincided with my mpg's for that tank.
Each vehicle is going to be different. On my first bar I get about 85 miles and each one is different after that. My ninth gets about 50 and the tenth gets about 20 before it starts to flash. I have only ran it down to the flashing tenth bar once and with my 2010 like my 2007 I usually get gas when I am down to two bars left. Some say that when you have the tenth start flashing you should have over 50 miles left, but I never want to chance it.
If they were real pips they would be a different color. I have found my computer is 10% off. When it says I'm getting 55mpg and I calculate it with the calculator, I find I am right at 50mpg. Every time, it is lower than what the car thinks I'm getting.
What I have done several times (as I usually will wait for the last one to start flashing myself), is drive another 100 miles or so after the flashing began. Then, when I fill up, I am only able to get 10 gallons into my tank. This means that if I am averaging 500 miles per fill-up, which I have not yet had a tank lower than that, and if I can only put in about 10 gallons, there must be 1.9 gallons left in the tank, or another 100 miles or so. While i usually try to fill-up as soon as I can after the flashing starts, I am not too worried. I only ran out of gas once in my life, when I was 17, and with my girlfriend. (But as she was wiser than I, I could not even take advantage of her.. j/k ) Her dad had to come help us, and I never did that again.
Pip Pip, n. [Formerly pippin, pepin. Cf. Pippin.] (Bot.) A seed, as of an apple or orange. [1913 Webster] -- From The Collaborative International Dictionary of English v.0.48 Pip Pip, n. [Perh. for pick, F. pique a spade at cards, a pike. Cf. Pique.] One of the conventional figures or "spots" on playing cards, dominoes, etc. --Addison. [1913 Webster]
