What is the pH to pOH Calculator?
This calculator converts a solution's pH into its pOH using the relationship that, in water at 25°C, pH and pOH always add up to 14. pH measures the acidity of a solution (the concentration of hydrogen ions, H⁺), while pOH measures its basicity (the concentration of hydroxide ions, OH⁻). Together they describe the same equilibrium from two complementary angles.
How to use it
Enter any pH value between 0 and 14 and the tool instantly returns the pOH. It also reports the hydrogen ion concentration [H⁺] and hydroxide ion concentration [OH⁻] in moles per liter, so you can see the full ionic picture of your solution at a glance.
The formula explained
The ion-product constant of water (Kw) is \(1.0 \times 10^{-14}\) at 25°C. Taking the negative logarithm of Kw gives \(\text{p}K_w = 14\), which equals \(\text{pH} + \text{pOH}\). Rearranging gives $$\text{pOH} = 14 - \text{pH}$$ The ion concentrations follow from \([\text{H}^+] = 10^{-\text{pH}}\) and \([\text{OH}^-] = 10^{-\text{pOH}}\).
Worked example
Suppose a solution has a pH of 3. Then $$\text{pOH} = 14 - 3 = 11.$$ The hydrogen ion concentration is \([\text{H}^+] = 10^{-3} = 0.001 \text{ mol/L}\), and the hydroxide ion concentration is \([\text{OH}^-] = 10^{-11} = 0.00000000001 \text{ mol/L}\). The low pOH confirms this is an acidic solution.
FAQ
Why does pH + pOH = 14? Because the ion-product of water (Kw) is \(10^{-14}\) at 25°C, and the negative logarithm of that constant is 14.
Does this hold at all temperatures? No. The value 14 is specific to 25°C. At higher temperatures Kw increases, so the sum becomes less than 14.
What pOH indicates a basic solution? A pOH below 7 indicates a basic (alkaline) solution, while a pOH above 7 indicates an acidic one.
