Can this be used for my tortoise
Unfortunately, this leash would not fit a tortoise because the leg holes are too close together. Thanks for asking!
What size would be good for a bearded dragon
The medium is a good fit for most adult bearded dragons of average size. If you have a very large bearded dragon you may want to try the large size.
What size would fit and avarage adult leopard gecko?
A small should work for an adult gecko. The leash size distance between the two front legs is up to 2 1/4" for the small. I am adding the other measurements to the product description for additional reference.