Again, this would depend on the type of holder you purchase. Smaller, more slimline options such as the visor tissue holder will be able to hold fewer tissues at a time – usually around the 50-tissue mark.
Meanwhile, the larger options, such as the Hanging Car Trash Can by HappyChappy, will be able to hold larger amounts in the hundreds. The Kleenex variety comes in canisters of 50, with 4 canisters in each pack.