Inside measurements are 5" wide x 8 1/2" deep x 5" tall

I was a little worried by the height too but so far my pastel seems to love them.
Gonna try some with my spider tonight.
The opening is wide so I sank them in the substrate so it wouldnt be as tall of an opening.

Funny thing is (his tank is close to the door going out into the garage) every time I open or close the door he looks out to see whats going on. We caught him watching my wife cooking dinner last night too. Then again he is our most sociable snake ever. Any time the lid comes off he will come out and climb your arm.