🧫Buffer pH Calculator
Use the Henderson-Hasselbalch equation to find buffer pH from pKa and conjugate acid/base concentrations.
Free Buffer pH Calculator
This buffer pH calculator applies the Henderson-Hasselbalch equation, pH = pKa + log([A⁻]/[HA]), to find the pH of a buffer solution made from a weak acid and its conjugate base. Enter the acid's pKa along with the concentrations of the conjugate base and weak acid, and the calculator returns the buffer pH along with the [A⁻]/[HA] ratio.
Buffers resist pH changes best when the ratio of base to acid is close to 1:1 (pH close to pKa) — this is where buffer capacity is highest. As the ratio moves away from 1:1, the buffer becomes progressively less effective at resisting further pH changes.
Useful for biochemistry, analytical chemistry, and lab buffer preparation. Free, runs entirely in your browser.
Frequently Asked Questions
What is the Henderson-Hasselbalch equation?
pH = pKa + log([A⁻]/[HA]), where pKa is the acid dissociation constant of the weak acid, [A⁻] is the conjugate base concentration, and [HA] is the weak acid concentration.
What is a buffer solution?
A buffer is a solution containing a weak acid and its conjugate base (or a weak base and its conjugate acid) that resists changes in pH when small amounts of acid or base are added.
What does pKa mean?
pKa is the negative log of the acid dissociation constant (Ka) — it indicates the pH at which a weak acid is exactly half dissociated (equal concentrations of acid and conjugate base).
When is a buffer most effective?
A buffer works best when the pH is close to the acid's pKa, ideally within about 1 pH unit — this is where the acid/base ratio is close to 1:1 and buffer capacity is highest.
What happens if [A⁻] equals [HA]?
The ratio is 1, log(1) = 0, so pH = pKa exactly. This is the point of maximum buffer capacity.
Can this calculator solve for concentrations instead of pH?
This version solves for pH given pKa and both concentrations. To target a specific pH, adjust the ratio of base to acid until the resulting pH matches your target.
Does buffer volume matter?
The Henderson-Hasselbalch equation depends only on the ratio of concentrations, not the absolute amounts, so diluting a buffer proportionally doesn't change its pH (though it does reduce buffer capacity).
What are common buffer systems?
Acetic acid/acetate (pKa ≈ 4.76), phosphate buffers, and Tris buffer (pKa ≈ 8.1) are commonly used in biochemistry and molecular biology labs.
Why use log base 10 and not natural log?
pH itself is defined using base-10 logarithms (pH = −log₁₀[H⁺]), so the Henderson-Hasselbalch equation consistently uses base-10 log as well.
Is this calculator free to use?
Yes, completely free with no sign-up, and it runs entirely in your browser.