pH measures how acidic or basic a solution is: pH = −log[H⁺], where [H⁺] is the hydrogen ion concentration in mol/L. Choose which value you know — [H⁺], [OH⁻], pH or pOH — and the calculator gives the other three.
Below pH 7 is acidic, 7 is neutral and above 7 is basic (alkaline), at 25 °C. For a strong acid like HCl, [H⁺] equals the acid's molarity; for a strong base like NaOH, [OH⁻] equals its molarity.
| I know the | [H⁺] concentration (mol/L) |
| Value | 0.001 |
| pH | 3 |
| pOH | 11 |
| [H⁺] (mol/L) | 0.001 |
| [OH⁻] (mol/L) | 1e-11 |
A 0.001 M strong acid has pH 3.
Try this example →| I know the | [OH⁻] concentration (mol/L) |
| Value | 0.01 |
| pH | 12 |
| pOH | 2 |
| [H⁺] (mol/L) | 1e-12 |
| [OH⁻] (mol/L) | 0.01 |
[OH⁻] = 0.01 M gives pOH 2 and pH 12.
Try this example →pH = −log₁₀[H⁺].
pH = 14 − pOH at 25 °C.
7 at 25 °C, where [H⁺] = [OH⁻] = 10⁻⁷ mol/L.
Yes, for very concentrated strong acids where [H⁺] is above 1 mol/L.