Different brands of cards will be slightly different sizes. The cheaper cards will be significantly different than higher quality cards. The cheaper cards, like Bicycle and various other generic brands, often use cheaper paper and/or worse coating so they can be much thicker. Most of the casino brands (Gemaco, Bee, Paulson, etc.) are pretty consistent. The casino cards will also start to swell and warp somewhat as they get used. It’s best to practice on a few different decks to get a feel for their differences.
-Sonny-