I have measured Jazz in JJ2 and he's somewhere between 2 and 3.5 bananas including ears, depending on whether you use large or small bananas for scale. I'll lean towards the latter, given how the large ones are used as pickups and might have therefore been made larger in manifestation of artistic freedom in order to make them noticeable, while the smaller ones are used in a more realistic situation of monkeys throwing them at you. That said, 3.5 bananas converts to roughly 70 centimeters, 53 excluding ears. The average length of a corgi measuring from their shoulders to the set on of the tail is about 39 centimeters. Unlike dogs, Jazz Jackrabbit is bipedal so it's not exactly easy to compare them but if we measure his height the same way, we get 29 centimeters. If we include the head, it's 44 centimeters instead. Either way, I'd say that using this set of data, Jazz is comparable to a corgi.

That would be it if not the fact we actually have a piece of official information regarding heights in JJ2 world. The official data sheet for Lori Jackrabbit informs that she is indeed 165 centimeters tall. This obviously screws things up and suggests that JJ2 universe contains some huge ass bananas. Anyway, if we believe this source (as is Dean Dodrill), Jazz is probably about 130 centimeters tall instead (from feet to the top of his head). This is not quite the size of an average adult human and I'd say there are dogs like that. Either way the vague phrase as is "dog size" sounds the most acceptable.