Peptide calculator

Our peptide calculator is a convenient tool for scientists as a molecular weight peptide calculator, which can be used as an amino acid calculator as well. Additionally, the tool includes a hydrophobicity calculator, a net charge calculator at different pH, isoelectric point calculator and the hydrophilicity ratio.

To use our peptide calculator mass properties, enter the sequence or the amino acid using 1-letter or 3-letter amino acid codes and our peptide calculator will provide the following physico-chemical properties of the sequence:

  • Molecular weight
  • Isoelectric point
  • Net charge at neutral pH (7.0)
  • Average hydrophilicity
  • Ratio of hydrophilic residues to total number of residues
  • Net charge vs. pH plot
  • Hydrophobicity plot

With the peptide calculator, it’s also possible to add N-terminal and C-terminal modifications to your peptide among Acetyl, Biotynil, pyroglutamic amino acid and amide.

Amino acid (3-letter code)Amino acid (1-letter code)
Amino acid (3-letter code)Amino acid (1-letter code)

How does the Peptide Calculator work?

The peptide calculator is one of the most useful tool for the peptide chemist to calculate peptide molecular weight and more. With the peptide calculator and its easy use, peptide chemists can have access to a molecular weight peptide calculator and amino acid calculator, the isoelectric point, a peptide net charge calculator at neutral pH, the average hydrophilicity, the percentage of hydrophilic amino acids, the plot of the net charge vs. pH and a hydrophobicity calculator displayed in a plot.

To calculate the different features of the peptide, the peptide calculator will apply the formulas described below:

For the peptide molecular weight calculator and molecular weight amino acid calculator, the following formula is applied:

M: Molecular weight of the amino acid sequence

Mn: Molecular weight of the N-terminus

Mc: Molecular weight of the C-terminus

Ni: Number of the amino acid residues

Mi: Molecular weight of the amino acid residues

For the molecular weight amino acid calculator, you can enter the 1- or 3- letter code of the desired amino acid, and the tool will provide the value the same way it would calculate peptide molecular weight.

The peptide net charge calculator at a given pH is based on the formula below:

Z: Net charge of the peptide sequence

Ni: Number of arginine, lysine, and histidine residues and the N-terminus

pKai, pKa: values of the N-terminus and the arginine, lysine, and histidine residues

Nj: Number of of aspartic acid, glutamic acid, cysteine, and tyrosine residues and the C-terminus

pKaj, pKa: values of the C-terminus and the aspartic acid, glutamic acid, cysteine and tyrosine residues

pH: pH value

The pKa values for cysteine (pKa = 8.33), aspartic acid (pKa = 3.86), glutamic acid (pKa = 4.25), histidine (pKa = 6.0), lysine (pKa = 10.53), arginine (pKa = 12.48), tyrosine (pKa = 10.07), the N-terminal (pKa = 9.69) and C-terminal (pKa = 2.34) are based on the Principles of Biochemistry, Lehninger (1982).

The isoelectric point calculator provides the pH at which the peptide net charge is zero. The isoelectric point is calculated by approximation (accuracy ± 0.01).

The calculation of the average hydrophilicity of a peptide is based on the data from Hopp&Woods. The hydrophilicity value for each amino acid in the peptide sequence is indicated in a bar graph. The ratio of hydrophilic residues to total number of amino acids is reported in %.

For more information on the peptide calculator, please read our details document.