S/M size fits up to 24", L obviously is bigger. They have elastic and the waistband can be adjusted with buttons.

One

This product is for a female dog. They're made quite differently.

China

This works much better than the disposable diapers that stretch out and can be shaken off. Make sure that you cut the tail hole in the right place and make sure that you don't cut it to big. I use cheap women's disposable panty liners in this, just make sure that you use the right absorbancy level for what you need. My dog is a great pyrenees/australian shepherd mix who is 82 lb and 26.5" around, she uses a L/XL. I would suggest a S/M based on the size chart. There are several buttons and velcro which allows for quite a bit of adjustment to insure that it fits properly. My dog has mild incontinence (leaking) and my vet started her on Proin 50mg for sphincter control and it worked for us, you might want to talk to your vet about it.

We order the ones from Barkertime... escape proof ones... our Frenchies eventually get out if anyone but they escape proof by Barkertime.. expensive but worth it 

Not for number 1’s it’s the other one 

Yes, there is a button hole type slit, and you simply use scissors to cut it open. For small tails you might not want to cut the entire length, hence the reason they allow you to cut it yourself.

For 16" waist, you must buy small or medium.