Acid-Base Calculator

Your details

Switch between buffer pH calculation and arterial blood gas interpretation.
Choose which variable to solve for; enter the other three.
Selecting a preset fills pKa automatically; you can still override it.
The measured or target pH of the buffer solution (0-14).
Acid dissociation constant expressed as -log10(Ka). Select a preset above or enter manually.
Molar concentration of the conjugate base (deprotonated form) in millimolar.
mM
Molar concentration of the weak acid (protonated form) in millimolar.
mM
Solved value
4.76

The calculated pH, pKa, [A-], or [HA] depending on the solve-for selection.

[A-] / [HA] ratio1
Result labelpH

Calculated buffer pH: 4.76

  • The [A-]/[HA] ratio is very close to 1, placing you right at the pKa: this is the optimal buffer point where pH is most resistant to change.
  • Buffer capacity is highest when pH is within one unit of pKa. Moving outside that range rapidly depletes the buffer.
  • The Henderson-Hasselbalch equation assumes ideal dilute solutions. At very high ionic strength or concentrations above ~0.1 M, activity coefficients diverge from 1 and the approximation becomes less accurate.

Next stepUse the ABG mode to interpret clinical arterial blood gas results and identify respiratory or metabolic acid-base disorders.

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