Henderson Hasselbalch Calculator
What approximate pH does an acid/conjugate-base buffer have? Enter the stated values to calculate this model.
Reference calculation or estimate for example inputs; assumptions and limitations apply.
Calculations run in your browser.
Assumptions / Standards / Limitations
Assumes a weak acid and its conjugate base with positive concentrations in matching units, small dissociation change relative to buffer-component concentrations and an appropriate pKa for temperature/ionic strength. It does not assess buffer capacity, strong-acid/base excess, concentrated-solution activity effects or biological/clinical samples.
Model reference: OpenStax Chemistry 2e; supplementary IUPAC definition where listed. Last verified: 2026-10-08. This is a scientific reference model; no regulatory code or installation standard is used.
Example inputs illustrate the calculation. They are not recommended preparation, installation or operating settings.
What to enter
| Input | Meaning and units |
|---|---|
| Acid pKa (1) | Enter acid pka in 1; use the same basis as the other measurements. |
| Conjugate base concentration (mol/L) | Enter conjugate base concentration in mol/L; use the same basis as the other measurements. |
| Weak acid concentration (mol/L) | Enter weak acid concentration in mol/L; use the same basis as the other measurements. |
Understanding your result
The result is a scientific reference calculation under the model assumptions on this page. It does not assess hazards, chemical compatibility, purity, solubility, equipment limits or clinical meaning.
Common mistakes
- Using solvent volume in place of final solution volume, or mass concentration in place of molar concentration.
- Ignoring units, reaction coefficients, activity assumptions or the stated temperature/model limits.
Check your calculation
- Check the units and balance/coefficients against the worked example. For real laboratory work, verify SDS information and the applicable procedure independently.
Calculation checks, sources and review limits
What approximate pH does an acid/conjugate-base buffer have?
What approximate pH does an acid/conjugate-base buffer have? Enter the stated values to calculate this model.
Common uses
- What approximate pH does an acid/conjugate-base buffer have
How it works
Add the base-10 logarithm of conjugate-base/acid ratio to the stated pKa. Both quantities must be positive; the buffer approximation does not apply universally to very dilute or extreme-ratio conditions.
Worked example
Enter Acid pKa: 4.76 1; Conjugate base concentration: 0.2 mol/L; Weak acid concentration: 0.1 mol/L. Results: Estimated buffer pH: 5.061029995663981 1.