Is it possible to calculate gas mileage for a lawn mower?
I figure there are variables, like what brand, make model you have, how large your yard is, etc etc I mean if I know I can go so far in my truck on a tank of gas, shouldn't I be able to figure the same out on something as simple as a lawn mower? This is giving me a headache.
hahaha!

You'd have to conduct an experiment to figure it out. Run the mower till it's completely empty. Put in exactly one gallon of gas – see how far you can go (I'd suggest doing this at a running track as opposed to driving your lawn mower down the street). Repeat this several times in different gears and different throttle levels.
You have too much time on your hands
Anything is possible, I once calculated the gas mileage for my VCR!
usually fuel consumption for gasoline engines is measured in gallons per hour.
Cut the grass, get a beer!
Just buy a goat !