pH is a measure of the hydrogen ion concentration of a solution. To calculate the pH of a solution you need to know the concentration of the hydronium ion in moles per liter. pOH is a measure of hydroxide ion (OH-) concentration. To calculate the pOH of a solution you need to know the concentration of the hydroxide ion in moles per liter. Use our online pH, pOH, [H+] and [OH-] calculator to calculate pH and pOH value based on the chemistry element and PH of density.