If my cat is 21 inches long does he really need a crate that’s longer than him?

Oh Aidan... If your cat is traveling 40 miles per hour on a train, how fast will he be traveling by paw walking the length of one train car?

And yes and seriously, it would be unethical to confine him to a coffin-like crate where he can't stand up for goodness knows how long while you go all over town socializing and being the life of the party. Give the cat room to breathe and to move around so he can feel like a person, not a commodity of fur.

Your cat has extra inches of diagonal space.

Depends on how long the drive is. But yes a cat needs to feel comfortable in the crate.

try another store maybe

If you need to cage him at least let him be comfortable.

W