Peptide Molecular Weight Calculator
Molecular Weight Calculator
Compute peptide MW from single-letter amino acid sequence.
Inputs
Frequently Asked Questions
Q1What is molecular weight and why is it important in peptide research?
Molecular weight (MW) is the sum of the atomic weights of all atoms in a molecule, expressed in daltons (Da) or g/mol. In peptide research, MW is used to verify compound identity, calculate molar concentrations, and convert between mass (mg/mcg) and molar amounts (nmol/pmol).
Q2How is the molecular weight of a peptide calculated from its sequence?
Sum the residue molecular weights of each amino acid, add 18.02 Da for the water molecule at the termini (H at N-terminus + OH at C-terminus), and the result is the peptide's MW. This calculator performs the summation automatically from your entered amino acid sequence.
Q3How do I convert between mcg and nmol for a peptide?
Use the relationship: mass (g) = moles × molecular weight (g/mol). For example, 1 nmol of a 3,500 Da peptide = 3,500 ng = 3.5 mcg. Conversely, 100 mcg of the same peptide = 100,000 ng ÷ 3,500 g/mol = 28.6 nmol. The calculator handles these conversions automatically.
Q4Does molecular weight affect how a peptide is absorbed or excreted?
Yes. Larger peptides (higher MW) generally have lower oral bioavailability due to poor GI absorption and enzymatic degradation. Renal clearance is also MW-dependent—peptides under ~30 kDa can be filtered by the kidneys, affecting half-life and excretion rate.
What This Calculator Does
The Molecular Weight Calculator looks up or calculates the molecular weight of common peptides and compounds used in research, and converts between molar (nmol/µmol) and mass (mcg/mg) quantities.
Formula Used
Moles (nmol) = Mass (mcg) ÷ Molecular Weight (g/mol) × 1,000Mass (mcg) = Moles (nmol) × Molecular Weight (g/mol) ÷ 1,000Example Calculation
Limitations
Molecular weight values are reference figures. Actual molecular weight may vary slightly depending on the specific salt form or modification of the peptide.