I'm receiving two Phyllomedusa Tomopterna (Super-Tiger Legged Monkey Frogs) from a breeder tomorrow and have an Exo Terra 12x12x18 (11 gallons) set up at their permanent home. I felt bad about the decision to get two at first as the home looked smaller once I actually purchased it, but I got the OK from the breeder for this size tank and if he says go for it then I trust him, he did raise the frogs after all. They get up to about 2 inches, or 2.5 for females, but have thin bodies and are not heavy.

I'd say go with what you're comfortable with without cramping your frogs TOO much. I gave the P. Tomopterna plenty of places to hide and climb and modified their background to make sure they'd have a place to perch and look around if they so desired. If I get them in there and they seem cramped, it will be a failure for me as I don't have another option at the moment, but for now I feel OK about it.

Just remember, frogs have survived under much worse conditions than these.