pOH is the negative base-10 logarithm of the hydroxide ion concentration: pOH = -log[OH-]. It measures the basicity of a solution; lower pOH means a more basic (alkaline) solution.

How is pH calculated from pOH?

At 25 °C, pH + pOH = 14 (derived from the water autoionization constant Kw = 1.0 × 10-14). So pH = 14 - pOH.

What concentration range is valid?

The formula is accurate for dilute aqueous solutions at 25 °C. Concentrations between 1 × 10-15 and 10 mol/L are accepted. Concentrations above 1 mol/L may deviate due to activity effects.

What does a pOH of 0 mean?

A pOH of 0 corresponds to [OH-] = 1 mol/L, which is a strongly basic solution (pH = 14). A pOH of 7 is neutral, and pOH above 7 indicates an acidic solution.

Can I enter scientific notation?

Yes. Enter values like 1e-5 or 2.5e-3. The tool accepts standard scientific notation and decimal formats.

Does temperature affect the result?

Yes. The relationship pH + pOH = 14 is specific to 25 °C. At other temperatures, Kw changes, so the sum differs slightly. This calculator assumes 25 °C standard conditions.

pOH Calculator

Enter a hydroxide ion concentration to instantly calculate pOH and derive the corresponding pH value.

Hydroxide Ion Concentration

Enter [OH^-] in mol/L. Accepts decimals or scientific notation (e.g. 1e-5).

[OH^-] (mol/L)

Quick examples

Enter a concentration and click Calculate to see results.

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Summary

The pOH Calculator computes the pOH of a solution from the hydroxide ion concentration [OH-] using the formula pOH = -log[OH-]. It then derives the pH using the relationship pH + pOH = 14 (valid at 25 °C). Enter a concentration in mol/L and get instant results for both values.

How it works

Enter the hydroxide ion concentration [OH-] in mol/L (e.g. 0.001 or 1e-5).
The tool applies pOH = -log₁₀([OH-]) to compute pOH.
pH is then derived using pH = 14 - pOH (at 25 °C, standard conditions).
The acidity or basicity of the solution is labeled automatically.
Copy any result with one click for use in reports or assignments.

Use cases

Verify pOH and pH calculations for chemistry homework or exams.
Check acid-base equilibrium values in lab reports.
Convert between [OH-] concentration and pH quickly.
Understand whether a solution is acidic, neutral, or basic.
Teach or learn the relationship between pOH and pH.
Cross-check titration endpoint pH values.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu