got a free tank

I am currently housing my 3 month old ball python in a plastic tub and will continue to do so for a while and today my friend gave me a free tank it is 31" x 11" and the glass at the front curves out about another 2" in the centre.

my question is how big will my ball python have to be before it can be moved into it and how big will it be before i have to move it out into a bigger tank?

thanks for the help! ;)

I wouldn't consider putting it into a tank that size until it's at least a year old, and closer to 3 feet. Of course there are some bps that don't take well to tanks after tubs. I had a new girl in a quarantine tank, who was used to racks and tubs. She did NOT eat well in the tank. Once she cleared quarantine and went into the rack she developed a SUPER feeding response!! Congrats on the free tank!