Peptide Calculator
Calculate peptide properties such as molecular weight, net charge at given pH, and extinction coefficient from amino acid sequence.
Published by:
isCalculator Editorial Team
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How to use this tool?
How to Use the Peptide Calculator
This tool calculates key properties of a peptide from its amino acid sequence. Follow these steps:
- Enter the sequence – Type the one-letter amino acid codes (e.g.,
ACDEFGHIKLMNPQRSTVWY) in the text area. Only uppercase letters A–Z are allowed; no spaces or numbers. - Set the pH – Enter a pH value between 0 and 14 (default is 7.0). This affects the net charge calculation.
- Specify cysteine bridges – If your peptide has disulfide bonds, enter the number of bridges (e.g., 1 for one S–S bond). This adjusts molecular weight and extinction coefficient.
- Click "Calculate" – The tool will validate inputs and display three results:
- Molecular Weight (Da) – Sum of residue weights plus water, minus 2.02 Da per bridge.
- Net Charge at pH – Calculated using Henderson-Hasselbalch for N/C-termini and side chains (R, K, H, D, E, C, Y).
- Extinction Coefficient (M⁻¹cm⁻¹) – Based on Trp (5500), Tyr (1490), and cystine bridges (125 each).
Note: All inputs are required. Invalid sequences or pH values will show an error. The formula explanation is displayed below results for reference.
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Frequently Asked Questions
A peptide calculator computes properties like molecular weight, net charge, and extinction coefficient from an amino acid sequence.
Molecular weight is the sum of the residue weights of each amino acid plus the weight of a water molecule (18.02 Da), adjusted for cysteine bridges.
Net charge is calculated using the Henderson-Hasselbalch equation for ionizable groups (N-terminus, C-terminus, and side chains) at the specified pH.