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pH and pOH Calculator

Enter any one of [H⁺], [OH⁻], pH or pOH and get all four values, an acidic/basic/neutral verdict, a visual position on the 0–14 scale, and the logarithm steps written out.

Try [H⁺] =

The formulas this tool uses

pH

pH = −log₁₀[H⁺]

pOH

pOH = −log₁₀[OH⁻]

Link at 25 °C

pH + pOH = 14

This tool uses simplified educational formulas and assumes standard conditions: 25 °C, dilute aqueous solutions, and full dissociation. Weak acids and bases need equilibrium (Ka/Kb) treatment beyond these formulas.

Understanding the answer

pH below 7 is acidic, exactly 7 is neutral, above 7 is basic. Because the scale is logarithmic, each unit is a 10× change in H⁺ concentration — lemon juice (pH ≈ 2) is a hundred times more acidic than tomato juice (pH ≈ 4).

Worked example

What is the pH of a 0.001 M solution of HCl (a strong acid)?

  1. HCl dissociates fully, so [H⁺] = 0.001 = 10⁻³ M.
  2. pH = −log(10⁻³) = 3.
  3. pOH = 14 − 3 = 11.

Answer: pH 3 — acidic, as expected for a dilute strong acid.

⚠ Common mistake: Scientific notation slips are the top error here: 1e-7 means 1 × 10⁻⁷. Typing 1-7 or 10-7 gives nonsense — use the “e” notation shown in the examples.

Frequently asked questions

What is the pH of pure water?

7 at 25 °C — [H⁺] is exactly 1 × 10⁻⁷ M from water's self-ionisation. At other temperatures neutral pH shifts slightly.

Can pH be negative?

Yes, for very concentrated strong acids ([H⁺] above 1 M). Everyday solutions stay within 0–14, which is why the scale is drawn that way.

How do I convert pOH to pH?

Subtract from 14 (at 25 °C): pH = 14 − pOH. A pOH of 3 means pH 11 — a basic solution.

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Learn the concepts

pH and pOH ExplainedUnderstand the pH and pOH scales: the formulas pH = −log[H⁺] and pH + pOH = 14, worked examples, and why each pH step means 10× the acidity.Molarity and Dilution ExplainedLearn molarity (M = mol/L) and dilution (C₁V₁ = C₂V₂) with worked examples, lab-style problems and the unit mistakes to avoid.What Are Ions?Ions are charged atoms formed by losing or gaining electrons. Learn cations vs anions, how to predict charges from the periodic table, and polyatomic ions.