Peptide molecular weight calculator
Enter a sequence in one-letter amino-acid codes. Use it to check the theoretical mass a CoA should report, or to compare analogues.
- Length
- 15 residues
- Monoisotopic mass
- 1,418.7041 Da
- Average mass
- 1,419.55 Da
- Net charge at pH 7.0
- -2.01
- Isoelectric point (pI)
- 3.68
- Extinction coefficient (280 nm)
- No Trp or Tyr: use 205 or 214 nm instead.
Standard residue masses are used. Charge and pI are estimates from textbook pKa values and can differ from measured values. Modified residues (fatty-acid chains, D-amino acids, cyclisation other than disulfides) are not included.
Frequently asked questions
What is the difference between monoisotopic and average mass?
Monoisotopic mass uses only the most abundant isotope of each element and matches the main peak in high-resolution mass spectrometry. Average mass weights every isotope by its natural abundance and is what low-resolution instruments and most labels quote.
Why does a C-terminal amide change the mass?
Replacing the C-terminal –OH with –NH2 lowers the mass by about 0.98 Da. Many peptide drugs and research peptides are amidated, so the option must match the real molecule.
How accurate is the calculated pI?
It is an estimate from textbook pKa values. Measured isoelectric points can differ by half a pH unit or more, especially for short or heavily modified peptides.
Peptide research tools
Where to buy
Why we send researchers to Nordapep
Comparing compounds is only half the job. The other half is knowing the vial contains what the label says. Nordapep publishes batch documentation for every compound it sells.
Browse the Nordapep catalogue →Each batch reference on the label matches its CoA, so you can check what is in the vial.
Enter the batch reference from your vial into Nordapep's batch-verification tool.
Purity is reported by RP-HPLC, the standard method for peptides of this size.
Bundled stacks for common comparisons, plus tiered pricing for volume orders.