Henderson-Hasselbalch Calculator
Use this Henderson-Hasselbalch calculator to estimate the pH of a buffer solution or the base-to-acid ratio needed for a target pH.
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Run the calculator.
What This Henderson-Hasselbalch Calculator Helps You Do
This page covers the two most common Henderson-Hasselbalch tasks: estimating buffer pH from a known conjugate pair, and solving for the ratio needed to reach a target pH. That makes it useful for both quick classroom checks and practical buffer setup.
The result text ties the number back to whether acid or base dominates, which is the main practical meaning behind the equation.
How to Calculate Henderson-Hasselbalch Calculator
- Choose the buffer calculation: Use pH mode when you know pKa and the conjugate base-to-acid ratio, or use ratio mode when you want the ratio required for a target pH.
- Enter pKa and concentration information: The ratio can be built either from actual concentrations or from the target pH difference from pKa.
- Apply the Henderson-Hasselbalch relation: The calculator uses a base-10 logarithm because that is how the pH and pKa scales are defined.
- Interpret the ratio: If pH equals pKa, the conjugate base and acid concentrations are equal. Higher pH requires more base relative to acid.
Henderson-Hasselbalch Calculator Formula
| Variable | Meaning | Unit |
|---|---|---|
| pH | Acidity of the buffer solution | pH units |
| pKa | Acid dissociation constant expressed as pKa | pKa units |
| [A-] | Conjugate base concentration | same concentration unit as acid |
| [HA] | Weak acid concentration | same concentration unit as base |
Use the worked examples below to check how the formula behaves with real values. If the result looks unexpected, verify the unit assumptions and the meaning of each variable before interpreting the answer.
Worked Examples
- pKa: 4.76
- Base concentration: 0.70 M
- Acid concentration: 0.50 M
Result: pH is 4.91.
Because base exceeds acid, the pH sits above the pKa.
- pKa: 7.20
- Base concentration: 0.40 M
- Acid concentration: 0.40 M
Result: pH is 7.20.
Equal conjugate pair concentrations make pH equal to pKa.
- Target pH: 8.00
- pKa: 7.40
Result: Required base/acid ratio is about 3.98.
A pH 0.60 units above pKa needs nearly four times as much base as acid.
- Target pH: 5.00
- pKa: 6.00
Result: Required base/acid ratio is 0.10.
A buffer one pH unit below pKa needs ten times more acid than base.
How to Interpret Your Results
| Range | Meaning | Action |
|---|---|---|
| Ratio below 1 | Acid exceeds conjugate base. | Expect pH below pKa. |
| Ratio equal to 1 | Acid and conjugate base are equal. | pH equals pKa for the ideal buffer relation. |
| Ratio above 1 | Conjugate base exceeds acid. | Expect pH above pKa. |
Frequently Asked Questions
References
Last reviewed: March 2026