pOH Calculator — pH, [H⁺], [OH⁻] from one input

pOH Calculator

Compute pOH, pH, [H⁺], and [OH⁻] from a single input. Default Kw=1.0×10⁻¹⁴ (25 °C). Use a custom Kw to model other temperatures/conditions.

pOH Calculator

This tool links pH, pOH, hydrogen ion concentration [H⁺], hydroxide ion concentration [OH⁻], and the ionic product of water Kw. At 25 °C, Kw=1.0×10⁻¹⁴ so pH+pOH=14, but Kw changes with temperature and composition; when Kw changes, the sum pH+pOH equals pKw=−log₁₀Kw, and the neutral point is pH=pKw/2. Pick a single known quantity—pH, pOH, [H⁺], or [OH⁻]—and the calculator derives the rest using base-10 logarithms. Concentrations spanning many orders of magnitude are rendered in scientific notation for readability, and you can switch between three and six significant figures. Minor differences after rounding can make [H⁺][OH⁻] deviate slightly from Kw; the consistency line indicates how close the product is to the chosen Kw.

How to use

  1. Choose a mode (Given pH, pOH, [H⁺], or [OH⁻]).
  2. Select Standard (25 °C) or enter a custom Kw.
  3. Enter your value and choose precision (3 or 6 significant figures).
  4. Click Calculate to see pH, pOH, [H⁺], [OH⁻], and pKw.
  5. Download a TXT summary or a one-page PDF.
Formula notes

pH = −log₁₀[H⁺];   pOH = −log₁₀[OH⁻];   pH + pOH = pKw (where pKw=−log₁₀Kw).
[H⁺] = 10^(−pH);   [OH⁻] = 10^(−pOH);   [H⁺][OH⁻] = Kw.

Disclaimer. Educational use only. Not a substitute for professional judgment.