Peptide Molecular Weight

Calculate peptide molecular weight, amino acid composition, and extinction coefficient from amino acid sequences

What is Peptide Molecular Weight Calculator?

A peptide molecular weight calculator computes the exact mass of peptides and small proteins from their amino acid sequences. It calculates both monoisotopic and average molecular weights, accounting for peptide bond formation and providing additional biochemical properties.

How to Use This Calculator

Quick guide to calculate peptide molecular weight:

  1. Enter amino acid sequence (single letter code)
  2. Results calculate automatically
  3. View composition table and properties
  4. Download or copy detailed results

When to Use

This tool is useful when you need to:

  • Calculate exact peptide mass for mass spectrometry
  • Determine amino acid composition and charge
  • Plan protein purification and analysis
  • Calculate extinction coefficients for quantification
  • Verify peptide synthesis results

Example Input

Sample His-tag sequence:

MGHHHHHH

Enter sequences with standard single-letter amino acid codes or use the Example button.

Example Output

Results include:

Monoisotopic Mass: 1024.42 Da Average Mass: 1024.96 Da Net Charge: +3.1 Extinction Coefficient: 5500 M⁻¹cm⁻¹

Plus detailed amino acid composition table.

FAQ

Q: What's the difference between monoisotopic and average mass?
A: Monoisotopic uses the most abundant isotope; average considers natural isotope distribution.

Q: How is net charge calculated?
A: Based on pKa values of ionizable groups at pH 7.0.

Q: What determines extinction coefficient?
A: Number of Trp, Tyr, and Cys residues that absorb at 280nm.