Isoelectric Point Calculator
Result
Isoelectric Point Calculator Estimate the isoelectric point (pI) of a peptide or protein from the pKa values of its ionizable groups. — free online calculator.
Formula
- Isoelectric Point Calculator calculates its result from Pka1, Pka2. It uses the formula pI = (pKa1 + pKa2) / 2 for adjacent ionizable groups. Change any input to recalculate the result instantly.
- The main inputs are pKa α-Carboxyl, pKa α-Amino, pKa Side Chain, Side Chain Type. Enter them in the units and format shown in the calculator.
- Use the units, labels and assumptions shown beside each input so the formula is applied consistently.
- Changing any input above recalculates the result with the same calculation engine used by this page.
Example: Isoelectric Point
- pKa α-Carboxyl: 2.2 C-terminus
- pKa α-Amino: 9.4 N-terminus
- pKa Side Chain: 0 0 if none
- Side Chain Type: none
Using Pka1 = 2, Pka2 = 3, the calculated result is 2.5.
Sample result: Calculating…
Frequently asked questions
What does the Isoelectric Point calculate?
Isoelectric Point Calculator Estimate the isoelectric point (pI) of a peptide or protein from the pKa values of its ionizable groups. — free online calculator.
Which values should I enter?
Enter pKa α-Carboxyl, pKa α-Amino, pKa Side Chain, Side Chain Type using the units and format shown beside each field.
What formula does this calculator use?
The calculator uses the following relationship: pI = (pKa1 + pKa2) / 2 for adjacent ionizable groups.
Why might my result differ from another source?
Results can differ when another source uses different units, rounding rules, conventions or assumptions. Compare the inputs and definitions before comparing results.
Does the result update automatically?
Yes. Changing an input updates the result using the same calculation engine shown on this page.