every one is different . but i knew one once that was huge, very nice indeed, especially when she lay on top of me, lots of french kising from her at the same time
My missus has some staffie in her. (Staffie X Pittie X Bull-Terrier) She's on the smaller side, about 28 or 29kg and accomodates me just fine. And I'm about average size. It will differ from one individual to the next. On smaller dogs correct prep and procedure is super important. And lots of lube.