Everything has its size and dimension even toilet paper roll dimensions will be important to know in relation to the use of it. The fact that there are many brands of toilet paper may well be affecting the size or dimension of the paper roll itself. When it comes to thing like covers for toilet paper rolls, surely the dimension should be understood.
As a matter of fact, 4” could be the common dimension of the toilet paper roll in term of its width as well as its diameter. There could be different dimensions in just 0.5” from that number mentioned previously.
Furthermore it is important to be able to think about the dimension easily when trying to find a replacement form other brands for example. So it is better to actually buy one brand of toilet paper roll in numbers so that there will be no problem in the future.
Some small toilets may need smaller version of such thing due to the fact that the available space is smaller. When buying the paper roll surely there is a chance to compare the size of many brands there on the spot so actually get the idea of the so-called standard dimension of such thing.