On a tank I will usually go 320 miles of which 80 or so is highway and the rest is 30mph city. My car is rated at 17 city and 27 highway.
One time I decided to do an experiment. Since I drive the exact same amount city/highway every tank I decided to try hypermiling and accelerating super-slow, not braking excessively, etc. It was tedious, heartwrenching, I got honked at a lot, and it made me want to murder babies.
End result? My car's computer reported 25mpg combined, but when I filled up I calculated I actually got more like 23mpg. Ugh.
It is now the next tank, and I've been driving normally. I'm not drag racing from every light, but I'm certainly not gingerly rolling away like I did the previous tank. End result? Car reports 24.5mpg, calculations after filling up say I got 23mpg.
I am so out of fucks to give.
Hilariously enough, I get 35mpg highway, which is higher than the car is supposed to get, with an engine that's got 210,000 miles on it. Must still be running efficiently.