Created By : Rina Nayak

Reviewed By : Phani Ponnapalli

Last Updated : Apr 03, 2023

Online Isoelectric Point Calculator is a free tool that helps to calculate the isoelectric point of a protein or chemical molecule effortlessly. Simply you have to give the dissociation constant of the base, the dissociation constant of acid to check the isoelectric point as output.

Enter dissociation constant of acid
Enter dissociation constant of acid

How to Find Isoelectric Point?

Go through the steps to calculate the isoelectric point of a molecule within no tme.

  • Obtain the dissociation constant of acid, dissociation constant of base of a chemical molecule.
  • Find the average of dissociation constants of acid and base to check the isoelectric point value.

What is Meant by Isoelectric Point?

The isoelectric point is the pH where the molecules are not having any net electric charge. So, the molecule is electrically neutral in its statistical mean value. The isoelectric point will affect the solubility of the molecules at the given pH. It is represented by pH(I), pI, IEP. In general, the net electric charge of the molecule is affected by the pH value of its surrounding medium.

Isoelectric Point Formula

The formula to compute the isoelectric point is given here:

pI = (pKa + pKb)/2


pI is the isoelectric point

pKa is the dissociation constant of the acid

pKb is the dissociation constant of the base


Question: Calculate the isoelectric point of Lysine.


Given molecule is Lysine

The dissociation constant of acid pKa = 8.95

The dissociation constant of base pKb = 10.53

Isoelectric point pI = (pKa + pKb)/2

pI = (8.95 + 10.53)/2

= 9.74

Therefore, the isoelectric point of Lysine is 9.74

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FAQ’s on Isoelectric Point Calculator

1. How to calculate the isoelectric point of a peptide?

A general thumb rule that works for peptides also works for amino acids. Find the value of pH where the net charge is zero and the average closest pKa value on either side. Get the pKa and pkb, get the average of those values to get the isoelectric point.

2. What is an isoelectric point for amino acids?

The isoelectric point for an amino acid is the point at which the amino acid has no net electrical charge. It is one of the important characteristics of the amino acid as every acid has at least two acid-base groups.

3. What is the importance of the isoelectric point?

The isoelectric point is important in protein purification as it represents the pH where solubility is typically minimal.

4. How to use the isoelectric point calculator?

Give data in the input fields i.e dissociation constant for acid, dissociation constant for the base. Press the calculate button to know the isoelectric point of the molecule.

Isoelectric Point Calculator