I gave this item as a gift and I am not sure what size tube he used. When I had one before, I used a larger one than I thought necessary so as not to have to blow it up to extreme. If you think a 14" tube would be good, get a 15" and so on. And whatever you do, don't let it in the sun for long periods of time. I found that no matter what, you have to get a new tube every year. Hope this helps.
Brad B Yes, it helped to know that. Thanks.