pH Calculator
Calculate pH, pOH, [H⁺], and [OH⁻] from a known value. Instant conversion between all pH scale quantities at 25 °C.
Relationships (at 25 °C)
pH + pOH = 14
pH = −log₁₀[H⁺] | pOH = −log₁₀[OH⁻]
The pH calculator enables conversion between pH value, pOH value, hydrogen ion concentration [H⁺], and hydroxide ion concentration [OH⁻]. All calculations apply at 25 °C, where the ion product of water Kw = 10⁻¹⁴.
The pH value is the negative base-10 logarithm of the hydrogen ion concentration: pH = −log₁₀[H⁺]. Together with the pOH value, the relationship pH + pOH = 14 holds. From any one of these four values, the other three can be calculated.
The pH value is one of the most important measurements in chemistry. It determines the acid or base strength of a solution and is crucial for chemical reactions, biological processes, water treatment, and industrial applications.