What this calculator does
Henderson–Hasselbalch (buffer pH) works out buffer pH from the acid dissociation constant and the base/acid ratio. 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
FormulapH = pKa + log₁₀([A⁻]/[HA])
The inputs explained
| Field | What to enter |
|---|---|
| pKa of the acid | A number. Starts at 4.76. |
| Conjugate base concentration [A⁻] (mol/L) | A number, measured in mol/L. Starts at 0.1. |
| Weak acid concentration [HA] (mol/L) | A number, measured in mol/L. Starts at 0.1. |
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 pka of the acid
Every other input is held at the calculator’s starting values while pka of the acid varies. Select any row to load that scenario into the calculator.