What is the pOH Calculator?
pOH measures the basicity of an aqueous solution on a logarithmic scale. This calculator converts between pOH, pH, hydroxide ion concentration [OH⁻], and hydrogen ion concentration [H⁺] using pOH = −log₁₀[OH⁻] and pH + pOH = 14 at 25 °C. Enter [OH⁻], a known pOH or pH, or the molarity of a strong base (e.g. NaOH, KOH) and get all related values instantly. Supports M, mM, µM, and nM. Runs in your browser with no signup.
How to use the pOH Calculator
- Choose a mode: [OH⁻] → pOH, pOH → ions, pH → pOH, [H⁺] → pOH, strong base, or strong acid.
- Enter the known value (scientific notation like 1e-7 works for concentrations).
- Select a concentration unit when the mode uses molarity or ion concentration.
- Read pOH, pH, [OH⁻], and [H⁺] in the results panel.
- Copy the summary for lab notes or homework.
Common use cases
- Finding pOH of 0.01 M NaOH (pOH = 2, pH = 12)
- Converting [OH⁻] = 1×10⁻⁷ M in pure water to pOH 7
- Getting pOH from a measured pH in titration or buffer problems
Frequently asked questions
- How is pOH calculated?
- pOH = −log₁₀[OH⁻], where [OH⁻] is the hydroxide ion concentration in mol/L. A lower pOH means a more basic solution.
- What is the relationship between pH and pOH?
- At 25 °C, pH + pOH = 14. If you know pH, subtract from 14 to get pOH, and vice versa.
- How do I find pOH of a strong base?
- For a strong monohydroxy base like NaOH, [OH⁻] equals the base molarity. Use Strong base mode or enter that concentration in [OH⁻] → pOH mode.
- When should I use pOH instead of pH?
- pOH is often more convenient for basic solutions — e.g. 0.01 M NaOH has pOH 2, which is easier to interpret than pH 12 in some lab contexts.
