Gas gauge is really off

That is very normal. Think of it as customer expectation management. All car makers do it.

For a variety of reasons, including an inherent inability of the car to accurately forecast upcoming fuel consumption conditions (which vary enormously in ways the car cannot possibly know in advance), some buffer or safety margin must be built into the display.

If it was truly accurate, many many many drivers would get caught pushing 'fumes' too far and run out of fuel along the roadside. The customer help line would be overwhelmed with angry calls from drivers declaring 'the car said I had enough gas to go there!', and not understanding why conditions changed after they passed the last filling station.

Based on my past cars, 100-ish miles of 'safety margin' seems normal.

 

mine is exactly the same. if you look at my stats in the spreadsheet sticky, you'll see most of my fill ups are 8 gallons, and that's at the flashing last bar and beep. you have another 100+ miles, but don't get caught with your pants down.

 

My rule of thumb assumes that I have at least 10 gallons of usable fuel in my tank after topping off. I then reset the trip ODO, so I can drive at least (10 X MPG) miles without running out. The blinking fool-gauge light is just a reminder to keep an eye on the ODO.

 

Most cars at cars made in the 90s and 2000s at E on the gas tank would still have about a gallon and a half or two left as a reserve. The Prius on 0 is just like any tank gauge on E. You still got miles to go before it runs dry. However, I definitely wouldn't recommend running it all the way down every time as have more gas in the tank helps disperse the heat for your fuel pump.