According to label it calls for 1.1 to 1.5 fl oz per gallon which covers approx 1000 sq ft in cool season grass applications. So if you go with 1.3 oz per gallon and do a little math... 128 oz per gallon. So divide 128 by 1.3 you get... 98.46ish. Multiply that by your 2.5 gallons you get 246.15. So you're pretty right on there.... So with your 246.15 gallons you can spray 246,150 sq ft, or 5.65 acres.
And if you have Trimec Classic Like I use around my house since I do not spray other persons properties and do not have proper licensing...you mix 1 oz per gallon and that treats 250sqft. so the one gallon you buy treats 32,000 sqft of cool season and warm season grasses. For St Augustine or Centipede grasses you still mix the same rate but coverage is twice as much... ie less chemical per area.
Of course always check the labels on your own chemicals cuz my information is about as accurate as what I get off of websites...and we can all believe everything we read on the internet...