How to figure out the mpg?

On the right hand instrument panel, where the Trip A and B info is displayed there should be Miles, then CONS and then MPH. CONS is the consumption in mpg.

The Prius display is optimistic by 5-7%. The easiest way to verify this is to reset either Trip A or Trip B each time you fill up. Before resetting, divide the miles driven by the number of gallons used to fill up for miles per gallon. After a few fillups a good average mpg can be determined and compared against the display mpg.

 

It is optimistically displayed on the TRIP A or B meter as CONS., it will say CONS. XX.X MPG. Use your steering wheel mounted Touch Tracer button marked TRIP on the right side to cycle through your TRIP Meter displays. They should go Odometer, TRIP A, TRIP B, DTE, no display, and back to ODO. Just remember the CONS. display is generious with its displayed MPG number if you hand jam the division it will be less, also it is only as accurate as when it was last reset.

Edit: I type to slow on my mobile JD scooped me, oh well.