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pOH Calculator
Convert between pH, pOH, and hydroxide ion concentration in one click using the standard aqueous equilibrium relationship.
What is pOH?
pOH measures the hydroxide ion concentration of an aqueous solution, just as pH measures the hydrogen ion concentration. It is defined as pOH = -log10[OH⁻]. In water at 25°C, pH and pOH always add up to 14, since pH + pOH = pKw = 14.
How this calculator works
Enter either a pH value or a hydroxide ion concentration. The calculator uses pOH = 14 – pH (when starting from pH) or pOH = -log10[OH⁻] (when starting from concentration), then derives the remaining values automatically.
Note: This tool is intended for general chemistry education and planning purposes, and assumes standard conditions (25°C, dilute aqueous solution).
Last reviewed August 2026