ANYONE KNOW THIS ANSWER?

it depends on the size, but usually, a tank for a bullfrog can be about 3' 6" to 6' in length and 2' to 3' in height. It depends on your frogs and what "personality" they have. Their personality is how active they are. the more active they are, the bigger tank they will need. If you go to your pet store, they will recomment the best one for them, but if they are pretty small, get one at least 2 1/2' in length.