A standard rule is that toilet paper holders are set about 26 inches above the floor. It should also be 10 inches in front of or next to the toilet.
Secondly, can you mount a toilet paper holder vertically?
This toilet paper holder is very easy to install but seems better suited for a horizontal installation. Here is why: when hung vertically, the tissue paper has no support underneath it, so it leans forward, causing the tissue to hang towards the floor.