What does pKa tell you?

pKa indicates acid strength on a logarithmic scale. Lower pKa means stronger acid. Each unit decrease in pKa represents a 10-fold increase in acid strength.

Yes. Strong acids like HCl have negative pKa values (around -7), meaning they dissociate almost completely.

How do I convert pKa back to Ka?

Ka = 10^(-pKa). For example, pKa = 4.76 gives Ka = 10^(-4.76) = 1.74 × 10⁻⁵.

Free pKa Calculator

Calculate pKa from the acid dissociation constant Ka, or convert between Ka and pKa values.

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Ka (Acid Dissociation Constant)

pKa

4.76

View formula & how it works →

How to Calculate pKa

Formula

pKa = −log₁₀(Ka)

Where:

pKa = negative base-10 logarithm of Ka

Ka = acid dissociation constant

A lower pKa indicates a stronger acid. pKa is more convenient than Ka for comparing acid strengths.

Example Calculation

Acetic acid has Ka = 1.75 × 10⁻⁵.

01pKa = -log₁₀(Ka)
02pKa = -log₁₀(1.75 × 10⁻⁵)
03pKa = 4.76

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