Buffer pH Calculator
Enter the pKa of the weak acid and the concentrations of the conjugate base and the weak acid to estimate the buffer's pH with the Henderson-Hasselbalch equation.
Last updated: September 26, 2026
Frequently asked questions
What is the Henderson-Hasselbalch equation?
It is pH = pKa + log₁₀([A⁻] / [HA]), relating a buffer's pH to the pKa of its weak acid and the ratio of conjugate base to acid concentration.
Why does equal acid and base give pH = pKa?
When [A⁻] equals [HA], the ratio is 1, and log₁₀(1) = 0, so pH = pKa exactly.
What is the effective buffering range?
A buffer resists pH change best within about one pH unit of its pKa, where the acid and conjugate base concentrations are within a factor of 10 of each other.
Does this equation work at any concentration?
It is most accurate for dilute solutions. At high concentrations, ionic strength affects activity coefficients and the simple concentration-based equation becomes less accurate.
How is this different from Buffer Capacity?
This calculator estimates pH from a buffer's composition. Buffer Capacity instead measures how much a buffer resists pH change when acid or base is added, from an observed pH shift.
Does this give a recipe for making a specific buffer?
No. It estimates pH from concentrations you supply and does not provide preparation instructions.
Is this the same as a Henderson-Hasselbalch Calculator?
Yes. "Buffer pH" and "Henderson-Hasselbalch" refer to the same equation and the same calculation, so this single page covers both names rather than splitting them into separate pages.