What Is the pH from pOH Calculator?
This tool converts a solution's pOH into its pH using the simple relationship \(\text{pH} = 14 - \text{pOH}\), valid for aqueous solutions at 25°C (298 K). pOH measures the hydroxide ion (OH⁻) concentration, while pH measures the hydrogen ion (H⁺) concentration. Because water self-ionizes with an ion product (Kw) of \(1 \times 10^{-14}\) at 25°C, the two scales always add up to 14.
How to Use It
Enter the pOH value of your solution and click calculate. The result shows the pH along with the corresponding hydrogen ion concentration [H⁺] and hydroxide ion concentration [OH⁻], both in moles per liter. A pH below 7 is acidic, exactly 7 is neutral, and above 7 is basic.
The Formula Explained
The relationship comes from the water equilibrium: \(\text{pH} + \text{pOH} = \text{p}K_w = 14\) at 25°C. Rearranging gives $$\text{pH} = 14 - \text{pOH}$$ The ion concentrations follow from the definitions \(\text{pH} = -\log[\text{H}^+]\) and \(\text{pOH} = -\log[\text{OH}^-]\), so \([\text{H}^+] = 10^{-\text{pH}}\) and \([\text{OH}^-] = 10^{-\text{pOH}}\).
Worked Example
Suppose a solution has pOH = 4. Then $$\text{pH} = 14 - 4 = 10$$ which is basic. The hydroxide concentration is \([\text{OH}^-] = 10^{-4} = 0.0001 \ \text{mol/L}\), and the hydrogen concentration is \([\text{H}^+] = 10^{-10} \ \text{mol/L}\).
FAQ
Why is the sum 14? Because the ion product of water (Kw) is \(1 \times 10^{-14}\) at 25°C, so \(\text{p}K_w = 14\). At higher temperatures this value changes slightly.
Can pH be negative or above 14? Yes. Very strong acids can give pH below 0 and very strong bases above 14, so the 0–14 range is just typical, not a hard limit.
Does this work at other temperatures? The formula \(\text{pH} = 14 - \text{pOH}\) is strictly correct only at 25°C. At other temperatures Kw differs, so the constant is no longer exactly 14.
