Hi! Welcome to DT from Colorado!
I'm not that familiar with crate sizes (I mean, I just use an old one I was gifted with if I need a crate; I have no idea how big it is officially….)
But I did find this info from Artemis on another thread:
In terms of crate size, I usually recommend a minimum of 42"ish for a comfortable fit for an adult dobe. Smaller individuals might fit into a 36-39" while growing up, or for transport purposes but they aren't going to be really comfortable for every day use. Luxury size for a dobe is gonna be 48" and over, and is truly ideal if the dog has to spend a lot of time in it even once grown.
Some crates come with dividers and barring that you can use cardboard boxes (covered in blankets) to put at the back of the crate for example.
I've also used plastic file boxes to take up room in the back of a crate to make it small enough for a puppy (in the housebreaking process you do NOT want to give them more room than they need when it's time to sleep, or they will go potty in that extra space when the need strikes.)
When I scan other threads, it looks like others here agree that 42" is adequate. I guess a big part of that decision is whether your grown dog will mostly be using it as an at-will sleeping den, or whether it will be crated for a substantial length of time. One thing I did with the one ADULT dog I had to leave crated for a longer period than I liked while I was at work was to set up an X-Pen in the kitchen so he could stretch his legs a bit.
With a puppy though, a crate is definitely the way to go—it can be hard to foresee what they might get into (and where there's a will, there's a way for these smart puppers) and the whole housebreaking thing is SO much easier, it is definitely worth it to accustom your dog to a crate.
Once mine got to be trustworthy though (somewhere around 8-9 months), they were allowed basic free run (just in a few dog-proofed rooms at first) But that ENTIRELY depends on the individual dog—some are never entirely trustworthy in the house alone, so it is worth it to be prepared.