Find buffer pH from pKa and the acid and conjugate-base concentrations using the Henderson–Hasselbalch equation.
Buffer pH
How to use this tool
Enter the weak acid pKa.
Enter the acid and conjugate-base concentrations in mol/L.
Read pH, the ratio and the percentage split.
Optionally enter a target pH to find its required ratio.
Formula & worked example
An acetic acid buffer with pKa 4.76 and equal 0.05 mol/L acid and base has pH 4.76; a 10:1 base-to-acid ratio gives pH 5.76.
Limitations — read this before you rely on it
Ideal-dilute approximation; it uses concentrations rather than activities and assumes the entered values are equilibrium concentrations.
Frequently asked questions
pH = pKa + log10([A−]/[HA]). It links buffer pH to the ratio of conjugate base to weak acid.
log10(1) is 0, so the ratio term vanishes and pH equals pKa — also the point of maximum buffer capacity.
Yes, if acid and base share the same solution volume, the volume cancels and the mole ratio equals the concentration ratio.
At very low or high pH, very dilute buffers, or high ionic strength, where activity corrections and water dissociation matter.
Pick an acid with pKa within about one unit of the target, then set the base/acid ratio to 10^(target pH − pKa), shown under Advanced options.