computer mpg seems very off

You are expecting far too much precision from the 'Guess Gauge", which bases its display only on the top 10 gallons or slightly less, not on the full 11.9 gallons.

The 2007 has a bladder in the tank, which adds considerable variability compared to other cars.

'Search' will find very many threads on this topic.

 

You're also assuming that the dealer filled it all the way up and not just high enough to show full. I can go well over 100 km before the guess gauge comes off full.

 

1) 11.9 gallons is the gross capacity, not the usable capacity. Figure somewhere around 10 gallons for actual usable capacity.

2) The gas gauge is not linear. Don't expect too much when trying to guess how much fuel remains. It's really not any better than any old analog gauge found in any other car.

3) The North American Gen II Prius models have a fuel tank bladder that causes some variation is usable capacity. This further exacerbates #2 above.

4) The MFD mileage is fairly accurate. Most owners find that it is about 3% optimistic.

Tom

 

Be honest. How accurately do you think you really know how much fuel was in that tank when you got it. Sorry to say but it could have been 9 gallons and still shown as full.

 

None of the cars that I ever drove ever had a "true linear" gas gauge. I usually manage to get about 60-75% of my miles from the first half of the tank...and the other half goes down pretty quickly. So don't rely on it too much.

 

+1, The only thing a gas gauge is good for is to tell you when it's time to get gas.

 

If you don't have one buy a copy of the 2007 Owner's Manual. It's full of info you need to know. And if you don't have a copy of Toyota's Scheduled Maintenance Guide, see here:
Toyota Parts and Service