What this calculator does
pKa from Ka works out calculates pKa from the acid dissociation constant Ka using pKa = -log10(Ka). Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulapKa = −log₁₀(Ka)
The inputs explained
| Field | What to enter |
|---|---|
| Acid dissociation constant (Ka) | A number. Starts at 0.000018. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with acid dissociation constant (ka)
Every other input is held at the calculator’s starting values while acid dissociation constant (ka) varies. Select any row to load that scenario into the calculator.
How the answer changes with acid dissociation constant (ka)
| Acid dissociation constant (Ka) | pKa | Ka used | Note |
|---|---|---|---|
| 0 | ∞ | 0 | A smaller pKa means a stronger acid (more dissociation at a given pH). |
| 0 | ∞ | 0 | A smaller pKa means a stronger acid (more dissociation at a given pH). |
| 0 | ∞ | 0 | A smaller pKa means a stronger acid (more dissociation at a given pH). |
| 0 | ∞ | 0 | A smaller pKa means a stronger acid (more dissociation at a given pH). |
| 0 | ∞ | 0 | A smaller pKa means a stronger acid (more dissociation at a given pH). |
| 0 | ∞ | 0 | A smaller pKa means a stronger acid (more dissociation at a given pH). |