A litter box should be deep enough to allow you to fill the litter box halfway with around 3 inches of litter.
The litter box should be easy for the cat to get into the litter box without any issue.
A standard size litter box that you can buy either online or in stores is the right size for a cat to use.
If the cat litter box is not deep enough then the cat may kick litter out of the litter box so make sure to use a deep enough litter box.
I would recommend just buying a litter box if you don't have one as they are made to the right size for the cat and they are not all that expensive for a regular litter box.
Also make sure to clean any poop out of the litter box daily and keep the litter box clean and change the litter every week or every month at least.