My 06 as a button on the end of the light stork pressing it cycles through mpg/miles since reset/miles left on tank instant mpg/ and
one or two I cant remember.
You can fill the car up. Drive it, monitor how many miles you have done and where the fuel gauge gets down to and then work out a rough idea of how much fuel you are using per bar on the gauge.
That is assuming you don't have the fuel computer as @RalphM has mentioned above.
The actual amount you have left is only ever an estimate, the type and style of driving you do will vary how much distance you can get out of an amount of fuel.