Will leave my original post up, but your
OP made it appear you knew nothing.
The rate per acre is pretty darn easy to figure out from the package. My memory is a half pint to pint per acre is a pretty common rate on most formulations, so I'd guess you had 20-40 acres worth there. Of course, that depends on the formulation, so read the label rather than rely on my wild-@$$ guess.
If you want to be 100% accurate, the calibration method up there is the way to go. If you want to ball park it, go to the web site of the nozzle manufacturer. They usually have charts that will tell you the gallons per acre at certain speeds and boom pressures.Tee Jet for example