What is the pH Calculator?
pH measures how acidic or basic an aqueous solution is. This calculator converts between pH, pOH, hydrogen ion concentration [H⁺], and hydroxide ion concentration [OH⁻] using the relations pH = −log₁₀[H⁺] and pH + pOH = 14 at 25 °C. Enter a known ion concentration, pH, pOH, or the molarity of a strong monoprotic acid or monohydroxy base (e.g. HCl, NaOH) and get all related values instantly. Supports M, mM, µM, and nM. Runs in your browser with no signup.
How to use the pH Calculator
- Choose a mode: [H⁺] → pH, [OH⁻] → pH, pH → ions, pOH → pH, strong acid, or strong base.
- Enter the known value (scientific notation like 1e-7 is supported for concentrations).
- Select a concentration unit when the mode uses molarity or ion concentration.
- Read pH, pOH, [H⁺], and [OH⁻] in the results panel.
- Copy the summary for lab notes or homework.
Common use cases
- Finding pH of 0.1 M HCl or 0.01 M NaOH in introductory chemistry
- Converting [H⁺] = 1×10⁻⁷ M (pure water) to pH 7
- Checking pH and [OH⁻] after entering a measured pOH value
Frequently asked questions
- How is pH calculated?
- pH = −log₁₀[H⁺], where [H⁺] is the hydrogen ion concentration in mol/L. A lower pH means a more acidic solution.
- What is the relationship between pH and pOH?
- At 25 °C, pH + pOH = 14 (pKw = 14). Knowing one lets you calculate the other and both ion concentrations.
- How do I find pH of a strong acid?
- For a strong monoprotic acid like HCl or HNO₃, [H⁺] equals the acid molarity. Enter that concentration in the Strong acid mode.
- Does this work for weak acids?
- No — weak acids only partially dissociate. Use Ka and an ICE table, or a dedicated weak-acid calculator, for accurate pH.
