MrBishop said:
If I wanted, I could have pulled up factory specs, but considering that the youngest of my cars is 9 years old, and not one of them have done anything resembling "average annual driving", they'd hardly be realistic or relevant. Specially since the van is on Toyo winters and the Colt Blizzaks. Either one of them is gonna drop your milage by a minimum of 5mpg.
Real milage is simple. Fill the tank. drive about, with the trip odo running. When you fill up, only fill to the automatic stop on the pump (do I need to tell you to use the same pump?) Don't advance to the round dollar either. Note the volume bought (yes, you can buy gas by something other than the $5. I don't do it very often either). Note the reading on the trip odo. Reset it. (what I like to do is to write the milage right on the receipt (you do get a receipt, don't you?))
Repeat this two more times.
Now, take the milage, and divide it by the volume to get your milage per volume. Do this for each one. Then add all the milage, and divide it by all the volume. See how this compares to the individual milages. This helps point out "bad" weeks, like when there's more construction, or more stupid people on the road.
Putting any faith in what the manufacturer, Gov't agency, or magazine tell you is the average milage ..... well, that's up to you.