Protein Molecular Weight & Composition Calculator

Calculate the precise molecular weight and amino acid composition of your protein or peptide sequence.

Enter your protein or peptide sequence using single-letter amino acid codes. Optionally, select N-terminal and C-terminal modifications, specify the number of disulfide bonds, and choose your preferred unit. This tool provides accurate results for research, lab work, and education.

Examples

Try these real-world protein and peptide sequences:

Insulin (Human, A Chain)

Protein

Insulin A chain with two disulfide bonds, no terminal modifications.

Amino Acid Sequence: GIVEQCCTSICSLYQLENYCN

Disulfide Bonds: 2

N-terminal Modification: None

C-terminal Modification: None

Result Unit: Dalton (Da)

Synthetic Peptide with Acetylation

Peptide

Short peptide with N-terminal acetylation and amidated C-terminus.

Amino Acid Sequence: ACDEFGHIK

Disulfide Bonds: 0

N-terminal Modification: Acetylation (Ac-)

C-terminal Modification: Amidation (-NH2)

Result Unit: Dalton (Da)

Lysozyme (Fragment)

Protein

Lysozyme fragment with one disulfide bond, no terminal modifications.

Amino Acid Sequence: KVFGRCELAAAMKRHGLDNYRGYSLGNWVCAAK

Disulfide Bonds: 1

N-terminal Modification: None

C-terminal Modification: None

Result Unit: Kilodalton (kDa)

Glutathione (GSH)

Peptide

Tripeptide with no modifications or disulfide bonds.

Amino Acid Sequence: GSH

Disulfide Bonds: 0

N-terminal Modification: None

C-terminal Modification: None

Result Unit: Dalton (Da)

Other Titles
Understanding Protein Molecular Weight & Composition Calculator: A Comprehensive Guide
Everything you need to know about calculating protein and peptide molecular weights.

What is Protein Molecular Weight?

  • Definition and Importance
  • How Molecular Weight is Calculated
  • Role in Biochemistry and Research
Protein molecular weight is the sum of the atomic masses of all atoms in a protein or peptide molecule. It is a critical parameter in biochemistry, molecular biology, and biotechnology, influencing protein purification, characterization, and functional studies.
Why is Molecular Weight Important?

Applications of Molecular Weight

  • Determining the size of proteins for SDS-PAGE.
  • Calculating dosages in pharmaceutical applications.

Step-by-Step Guide to Using the Calculator

  • Inputting Your Sequence
  • Selecting Modifications
  • Interpreting Results
To use the calculator, enter your protein or peptide sequence using single-letter amino acid codes. Select any N-terminal or C-terminal modifications, specify the number of disulfide bonds, and choose your preferred result unit. The calculator will instantly provide the molecular weight and composition.
Tips for Accurate Results

Best Practices

  • Use only standard amino acid codes (A, C, D, E, etc.).
  • Double-check the number of disulfide bonds.

Real-World Applications of Protein Molecular Weight Calculation

  • Laboratory Research
  • Pharmaceutical Development
  • Bioinformatics Analysis
Molecular weight calculations are essential in protein purification, mass spectrometry, drug design, and computational biology. Accurate mass determination helps in identifying proteins, designing experiments, and interpreting results.
Where is This Calculator Used?

Use Cases

  • Protein identification in mass spectrometry.
  • Designing synthetic peptides for research.

Common Misconceptions and Correct Methods

  • Misreading Amino Acid Codes
  • Ignoring Modifications
  • Incorrect Disulfide Bond Counting
A common mistake is entering non-standard amino acid codes or forgetting to account for modifications and disulfide bonds. This calculator ensures only valid inputs are accepted and all relevant factors are included in the calculation.
Avoiding Calculation Errors

Tips to Avoid Mistakes

  • Always use single-letter codes.
  • Include all modifications and bonds for accuracy.

Mathematical Derivation and Examples

  • The Calculation Formula
  • Worked Example
  • Interpreting the Output
The molecular weight is calculated as the sum of the masses of all amino acids in the sequence, minus the mass of water (18.01528 Da) for each peptide bond, plus or minus any modifications. Disulfide bonds further reduce the total mass by 2.0156 Da per bond.
Example Calculation

Calculation Examples

  • Sequence: ACDEFGHIK, N-term: Acetylation, C-term: Amidation, Disulfide: 0, Unit: Da.
  • Result: Accurate molecular weight and composition displayed.