Science · Chemistry / Acid–Base

pH Calculator

Enter a pH, pOH, hydrogen ion concentration or hydroxide concentration and get all four values instantly, with an acid / base classification.

[H³⁶] · mol/L

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pOH

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[H³⁶]

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[OH⁻]

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Acid–base definitions

pH = −log₁₀[H³⁶] pOH = −log₁₀[OH⁻] K_w = [H³⁶][OH⁻] = 1.0×10⁻¹⁴

pH is the negative base-10 logarithm of the hydrogen ion concentration in mol/L. Water autoionises with K_w = 1.0 × 10⁻¹⁴ at 25 °C, so pH + pOH = 14 and each pH step represents a tenfold change in acidity.

🔢 Four entry modes

Start from pH, pOH, [H³⁶] or [OH⁻] — whatever you have.

🤯 Classification

Neutral, acidic or basic at 25 °C, colour-coded instantly.

📈 Worked steps

Every logarithm step shown with base-10 conversion.

🌡 Tenfold intuition

See the concentration behind every pH point, from 1 · 10⁻¹⁴ to 1.

More acid–base & chemistry

Concentrations and buffers rely on molarity math.

Molarity Calculator