A terrier-brained escape artist in a small body
Miniature schnauzers are 11–20 lb, so the 22" or 24" crate fits. What sets the breed apart is temperament: they're terrier-descended, opinionated, vocal, and surprisingly determined about defeating crates. A mini schnauzer that decides the crate is boring will chew door hinges, work latches, and dig at pans. Two-point latching and a mid-grade crate rather than the cheapest small wire model.
They also bark. A lot. At everything. Position the crate away from windows and doors, and understand that some barking is genetic rather than trainable.