Isoelectric Point (pI) Calculator

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Choose a standard amino acid for instant lookup, or enter your own pKa values for any molecule.
All 20 standard proteinogenic amino acids with published pKa values from Lehninger.
Enter a physiological or experimental pH to see the net charge at that point.
Isoelectric Point (pI)Near-neutral pI
6.02

pH at which the molecule carries zero net electrical charge

pKa1 used2.34
pKa2 used9.69
Net charge at checked pH-0.005
Charge characterNegative (-0.005)
Amino acid classNonpolar
6.02 pH
Strongly acidic<4Acidic4-6Near-neutral6-8Basic8-10Strongly basic10+

Isoelectric point: pH 6.01

  • At pH 6.01, Alanine carries zero net charge and is in its zwitterionic form.
  • At your check pH of 7.4, the molecule is negatively charged (pH is above pI, so protons are released).
  • Molecules are least soluble at their pI because zero net charge reduces electrostatic repulsion between molecules, promoting aggregation or precipitation.

Next stepIn protein electrophoresis, a protein migrates toward the electrode whose charge is opposite to its own; at pI it stops moving. Use this pI to select the right pH buffer for isoelectric focusing (IEF) or ion-exchange chromatography.

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