Amino Acid Molecular Weight Calculator

The Amino Acid Molecular Weight Calculator computes the mass of a protein or peptide from its sequence — useful in biochemistry for characterizing proteins, designing experiments, or verifying synthesis results. Enter your protein/peptide sequence using single-letter or three-letter amino acid codes, then select any N-terminus and C-terminus modifications to get the molecular weight in Daltons. Secondary outputs include total amino acid count, average residue weight, and extinction coefficient at 280nm.

Use single letter amino acid codes (A, C, D, E, F, G, H, I, K, L, M, N, P, Q, R, S, T, V, W, Y)

Results

Molecular Weight

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Total Amino Acids

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Average Residue Weight

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Extinction Coefficient (280nm)

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Results Table

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Frequently Asked Questions

What can the amino acid molecular weight calculator be used for?

This calculator can be used to determine the molecular weight of proteins, peptides, and amino acid sequences. It's useful for protein analysis, gel electrophoresis planning, mass spectrometry verification, and biochemical research applications.

How do you calculate peptide molecular weight?

Peptide molecular weight is calculated by summing the molecular weights of all constituent amino acids, subtracting water molecules lost during peptide bond formation, and adding terminal group weights. The formula is: MW = Σ(amino acid weights) - (n-1) × 18.015 + terminal modifications.

How does the peptide and amino acid calculator work?

The calculator parses your input sequence, identifies each amino acid, looks up standard atomic weights, accounts for peptide bond formation (water loss), and includes any specified terminal modifications. It provides both total molecular weight and detailed composition analysis.

What sequence formats are supported?

The calculator supports both single-letter amino acid codes (A, C, D, E, etc.) and three-letter codes (Ala, Cys, Asp, Glu, etc.). Single-letter format is most commonly used and recommended for longer sequences.

How can terminal modifications affect molecular weight?

Terminal modifications significantly impact molecular weight. N-terminus modifications like acetylation (+43 Da) or formylation (+29 Da), and C-terminus modifications like amidation or esterification can add substantial mass to your peptide or protein.

What is the extinction coefficient and why is it important?

The extinction coefficient at 280nm indicates how strongly your protein absorbs UV light, primarily due to tryptophan and tyrosine residues. This value is crucial for determining protein concentration using UV spectrophotometry.

Can this calculator handle modified amino acids?

Currently, the calculator handles standard proteinogenic amino acids and common N/C-terminal modifications. For non-standard amino acids or post-translational modifications, you may need specialized software or manual calculations.