pH and pOH calculator
Calculate pH, pOH, [H⁺] and [OH⁻] from any one of them or from the concentration of a strong acid or base, and see whether the solution is acidic, neutral or basic at 25 °C.
pH, pOH and ion concentration
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pH and pOH calculator: what it is for
Choose what you know (pH, pOH, H⁺ or OH⁻ concentration, or the concentration of a strong acid or base) and type the value. The tool calculates the rest with pH + pOH = 14 at 25 °C, classifies the solution as acidic, neutral or basic and marks the result on the 0 to 14 scale. For very dilute strong acids and bases, it accounts for water's self-ionization.
The calculations run in your browser.
How to use
- Choose the value you have.
- Type the value.
- See pH, pOH and the concentrations.
When to use it
- Solve ionic equilibrium exercises.
- Check lab solutions.
- Understand the pH scale.
Frequently asked questions
How is pH calculated?
pH = −log[H⁺], where [H⁺] is the hydrogen ion concentration in mol/L. A solution with [H⁺] = 0.001 mol/L has a pH of 3. At 25 °C, pH + pOH = 14.
What about a strong acid?
Strong acids like HCl and HNO3 ionize completely, so [H⁺] equals the acid concentration times the number of ionizable H. In very dilute solutions, the tool includes water's self-ionization so an acid never gives a pH above 7.
What does pH 7 mean?
It is the neutral pH of pure water at 25 °C. Below 7 the solution is acidic and above 7 it is basic (alkaline). Each pH unit is a 10 times higher or lower H⁺ concentration.
Is it really free?
Yes, 100% free. No sign-up, no subscription and no usage limits. All Tools123 tools are free and run right in your browser.