It's maybe and inch to an inch and a half. I am measuring it with a Ryobi temp gun. I do not have anything to measure the ambient temp yet. I have Acu-rite and two Ranco thermostats on order. I was just trying to get things going as much as I could before I actually get the snake. I just pushed the bedding aside and the glass was 106. So yea, I guess I missed the obvious on that one. I have a Neodeshia 36" cage but I think thats too big for a baby. I'm getting a 2011 hatchling.