pH Calculator

Convert between pH, pOH, [H⁺] and [OH⁻] for aqueous solutions at 25 °C.

What Do You Want to Find?
Fractions and decimals both work.
–
pH
pOH
[H⁺]
[OH⁻]
Acidic or basic
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pH Formulas

pH = −log₁₀[H⁺]   pOH = −log₁₀[OH⁻]   pH + pOH = 14 (at 25 °C)

Worked Example

Tips

Each pH unit is a tenfold change in hydrogen ion concentration. pH + pOH = 14 holds at 25 °C; at other temperatures water’s ionization constant changes (at 37 °C, neutral pH is about 6.8). This page uses concentration, not activity, which is fine for dilute solutions.