I really matters on a lot of factors like tires, presure, condition of bike, outside tempurature, riding style, trails or road miles and many other factors. With that being said i´v gotten up to 48 mpg on my DT250 with the stock tires pumped up hard and only highway miles with a steady speed of 45 mph. But with my new tires and I run them very low on presure and ride both trails, hillclimbs, and road miles I now get around 28 mpg on average but have gotten as low as 12 mpg when riding strictly in the gravel pit climbing soft sand hills all day. The best way to calculate your mpg is to gas up and reset your miles. Then take the number of miles driven divided by the gallons of gas it took to refill the next time you hit the pump.