Peptide Properties Calculator

Peptides are short chains of amino acids used in drug development, research, and diagnostics — and their physical properties determine how they behave in solution and in the body. Enter your peptide sequence using single- or three-letter amino acid codes, optionally add N-terminal or C-terminal modifications (such as acetylation, amidation, or biotin), and set your pH to get the molecular weight, net charge, isoelectric point (pI), hydrophobicity, and extinction coefficient. Also try the calculate Antibody Volume Needed, Buffer Volume Needed & Dilution Factor — Western Blot Antibody Dilution.

Results

Molecular Weight

Net Charge

Isoelectric Point (pI)

Hydrophobicity

Extinction Coefficient

What can the peptide calculator be used for?

The peptide calculator can be used to determine key properties of peptides including molecular weight, net charge at specific pH, isoelectric point, hydrophobicity index, and extinction coefficient. These properties are essential for peptide synthesis, purification, and characterization. See also our use the ELISA Calculator.

How do you calculate peptide charge?

Peptide charge is calculated by summing the charges of all ionizable amino acid residues at a given pH. Each amino acid has specific pKa values for its ionizable groups, and the Henderson-Hasselbalch equation is used to determine the fractional charge at the specified pH.

How do you calculate the net charge of a peptide?

Net charge is calculated by adding the positive charges (from basic amino acids like lysine, arginine, histidine) and subtracting the negative charges (from acidic amino acids like aspartic acid, glutamic acid) at the specified pH, including contributions from the N- and C-termini.

How do you calculate peptide molecular weight?

Peptide molecular weight is calculated by summing the molecular weights of all amino acid residues and subtracting the molecular weight of water for each peptide bond formed (n-1 water molecules for n amino acids). Terminal modifications are also included in the calculation. You might also find our Annealing Temperature Calculator useful.

How do you calculate the isoelectric point of peptides?

The isoelectric point (pI) is the pH at which the peptide has a net charge of zero. It's calculated by finding the pH where the sum of all positive and negative charges equals zero, using iterative calculations with the Henderson-Hasselbalch equation.

What is peptide hydrophobicity and how is it calculated?

Hydrophobicity indicates how well a peptide interacts with water versus hydrophobic environments. It's calculated using hydrophobicity scales that assign values to each amino acid based on their tendency to partition between water and organic solvents.

How can the calculator identify peptide purity?

While the calculator doesn't directly measure purity, it provides theoretical molecular weight and extinction coefficient values that can be compared with experimental data from mass spectrometry and UV spectroscopy to assess peptide purity and identity.

What amino acid modifications are supported?

The calculator supports common N-terminal modifications (acetylation, 5-FAM, biotin) and C-terminal modifications (amidation, biotin, benzyl). These modifications affect the molecular weight and can influence the peptide's charge and other properties.