pH Calculator

This calculator finds the pH of an aqueous solution five ways: from the concentration of an acid, from the concentration of a base, from the mass and volume of an acid or a base, or directly from ion values ($[\mathrm{H}^+]$, $[\mathrm{OH}^-]$, or pOH). Along with pH it reports the matching ion concentrations, pOH, and the pKa or pKb of the compound involved.

It is built for students checking homework, lab staff preparing reagents, and anyone who needs a quick acidity answer without solving logarithmic equations by hand. Pick one of 22 common acids or 7 common bases — each comes with its published ionization constant and molar mass — or choose the custom option and enter your own Ka or Kb.

Worked example: 0.1 M formic acid

Formic acid ($\mathrm{HCOOH}$) has $\mathrm{Ka} = 0.00018$. Select it, enter a concentration of 0.10 M, and the calculator solves the equilibrium for the hydrogen ion concentration first:

The matching pOH is 11.62 and the hydroxide concentration is about $2.4 \times 10^{-12}\ \mathrm{M}$ — exactly what the Related numbers section shows.

Quick check from ion values

If you already know one ion value, switch to the ion option and enter it. Typing a pH of 4 immediately gives $[\mathrm{H}^+] = 10^{-4}\ \mathrm{M}$, a pOH of 10, and $[\mathrm{OH}^-] = 10^{-10}\ \mathrm{M}$.

Weak acid or base equilibrium

Mass and volume to concentration

pH, pOH, and ion concentrations

The ion option solves this network in every direction: enter any one of pH, $[\mathrm{H}^+]$, pOH, or $[\mathrm{OH}^-]$ and the other three follow. The same network runs behind the acid and base modes, which is why every calculation also reports pOH and hydroxide concentration.

Need the pH of a buffer mixture rather than a single acid or base? Continue with the buffer pH calculator. If you need to prepare the solution at a target molarity first, the molarity calculator walks through the same mass–volume–concentration conversion step by step.