pH or (pOH) only ranges from 0-14.
It measures the amount of hydronium or hydroxide ions (respectively).
The range of pH was determined from the neutral state of water which has 10-7 mol of Hydronium and 10-7 mol of Hydroxide.
Respectively, there are the H+ and OH- levels.
Then, they were just added up.
The lower it is on pH, the more acidic.
The higher it is on pH, the more basic.
The opposite occurs with the pOH.