It depends on what size you get .... I had a Ninja 250 that averaged about 70 mpg. Then I had a Katana that only got about 33 mpg. I can't imagine that even a ZX14 would get below 30. Of course bike gas mileage is just like car gas mileage, it all depends on how you ride. But assuming it's all stock and you ride like you have sense Then here's an estimation ....
250cc - 70mpg
600cc - 40mpg
750cc - 35ish mpg
1000cc - 31mpg
and the rest will probably hang around the 30mpg mark.