Ka to pKa Calculator

About this calculator

The acid dissociation constant (Ka) measures how completely a weak acid ionizes in water — a larger Ka means a stronger acid. Because Ka values span many orders of magnitude (from 10⁻¹ down to 10⁻¹⁴ or smaller), chemists convert them to a logarithmic scale using pKa = −log₁₀(Ka), the same transform used for pH. On this scale, a lower pKa indicates a stronger acid, and the values are compact enough to compare and tabulate easily.

Chemistry students and instructors use pKa constantly when studying acid-base equilibria, buffer solutions, and the Henderson-Hasselbalch equation, while pharmaceutical chemists rely on it to predict how a drug's ionization state — and therefore its solubility and absorption — changes with pH. Analytical and organic chemists likewise reference pKa tables to choose appropriate buffers or predict reaction behavior.