http://www.fueleconomy.gov/
The actual mpg you will get on a car varies according to how you drive it.
I think the current scheme for assigning mpg ratings is deceptive, because it tries to "take into account" inefficient driving styles.
I think this was unnecessary, and tends to soft pedal the difference between high and low efficiency cars. Which I suspect was probably the whole point of switching the method.
I preferred the old method, which used a more strictly standardized test.
Your Honda Accord's numbers are "18/25 mpg," for example.
But according to the old standard, the numbers are "20/28 mpg."
And from my experience I'd say you can very likely get something close to those old standard numbers, if not slightly better, if you drive efficiently.