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Peptide Molecular Weight Reference: Formula, MW, CAS and Sequence Length

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Published by Pepora (peporalabs.com). We earn when you buy with our code, which is why everything here is verifiable at the lab's own source, not on our word.

Peptide Molecular Weight Reference: Formula, MW, CAS and Sequence Length

This page gives you the molecular formula, molecular weight (in g/mol / daltons), amino-acid sequence length, CAS number, and salt-form note for every research peptide coaindex covers, each value cross-checked against PubChem and DrugBank rather than copied from a vendor listing. The deciding point to carry into every row below: a molecular weight is only as trustworthy as the third-party COA and the mass-spec trace behind it. A catalog number tells you what the ideal molecule weighs; a real vial’s certificate tells you what is actually in it, at what purity, and in which salt form. Use this table to know what the number should be, then use the certificate to confirm the vendor hit it.

Published 2026 - For research use only (RUO). Nothing here is medical advice, a dosing protocol, or a human-use recommendation.

The molecular-weight reference table

Values are for the free base / free acid unless the salt-form note says otherwise. Weights are average molecular weights (the figure catalogs list); a mass spectrometer on a COA reports the monoisotopic mass, which runs a few daltons lower on the larger peptides.

Compound Molecular formula Molecular weight (g/mol) Sequence length (aa) CAS number Salt-form note
BPC-157 C62H98N16O22 ~1419.5 15 137525-51-0 Free base. Usually shipped as acetate salt (C64H102N16O24, ~1479.6), a separate PubChem record with more mass per molecule.
TB-500 (Thymosin Beta-4) C212H350N56O78S ~4963.5 43 77591-33-4 Free acid, N-terminally acetylated. Typically supplied as acetate/TFA salt. PubChem indexes it under the INN “timbetasin.”
GHK-Cu (copper tripeptide-1) C14H24CuN6O4 ~403.9 3 89030-95-5 Copper(II) complex. Uncomplexed GHK tripeptide is C14H24N6O4, ~340.4. Some sources instead write the deprotonated complex C14H22CuN6O4 (~401.9) - see notes below.
Tesamorelin C221H366N72O67S ~5135.8 44 218949-48-5 Free base. N-terminal trans-3-hexenoyl group. Supplied as acetate. DrugBank DB08869.
Epitalon (epithalon) C14H22N4O9 ~390.4 4 307297-39-8 Free acid (Ala-Glu-Asp-Gly). Often supplied as acetate.
Thymosin Alpha-1 (thymalfasin) C129H215N33O55 ~3108.3 28 62304-98-7 N-terminally acetylated free acid. Supplied as acetate.
ARA-290 (cibinetide) C51H84N16O21 ~1257.3 11 1208243-50-8 N-terminal pyroglutamate. Supplied as acetate.
GLP-3 RT (GLP-class research peptide) C221H342N46O68 ~4731.3 (a minority of listings say ~4894.6 - verify) 39 2381089-83-2 Fatty-acid-modified. Consensus figure is 4731.3; confirm against the specific COA and mass-spec trace.

How to read and use this data

Each row answers a different question, so read the columns for what they are:

  • Molecular formula is the atom count for one molecule of the ideal, pure peptide. A COA’s mass-spec section should resolve to a mass consistent with this formula. If it does not, that is a flag.
  • Molecular weight is what one mole weighs. The figures here are average weights. Your COA almost certainly reports a monoisotopic mass from the mass spectrometer, which is the sum of the single most-abundant isotope of each atom. For a small peptide like Epitalon the two agree within a fraction of a dalton; for TB-500 or Tesamorelin the monoisotopic mass sits several daltons below the average. Neither is wrong; they are two conventions. Compare the COA’s number to the correct convention before you call a mismatch.
  • Sequence length is the amino-acid count. GHK-Cu is a genuine 3-mer with a metal ion; the large “thymosin” and GRF-analog entries are 28-44 residues, which is why their weights are an order of magnitude higher than BPC-157.
  • CAS number is a registry identifier, not a proof of identity or purity. A correct CAS on a label means the vendor knows what molecule they claim to sell. It says nothing about whether the powder in the vial matches. Only the accession-verifiable COA closes that gap - see how to verify a peptide COA by lookup.
  • Salt-form note is the column most people skip and the one that most often explains a “wrong” weight. Read it before you conclude anything from a mass number.

Sourcing and accuracy

Where each value comes from, and where it is soft:

  • Formulas, average MWs, and CAS numbers for BPC-157, TB-500, GHK-Cu, Tesamorelin, Epitalon, Thymosin Alpha-1, and ARA-290 are drawn from PubChem compound records and, for Tesamorelin, DrugBank (DB08869). These are the free-base / free-acid values. See the References.
  • Salt form vs free base. PubChem lists both a free-base entry and an acetate-salt entry for several of these peptides. BPC-157 acetate is a separate CID with formula C64H102N16O24 at about 1479.6 g/mol, roughly 60 daltons above the free base. The counter-ion mass means a vial filled as acetate contains slightly less net peptide than its gross weight suggests. This is normal, not fraud, but it is why gross vial mass and COA free-base mass can differ.
  • Average vs monoisotopic. Every weight in the table is an average molecular weight. Do not compare it directly to a mass-spec peak, which is monoisotopic; the larger the peptide, the larger the honest gap between the two.
  • GHK-Cu copper accounting. PubChem’s record for the copper complex (CID 378611) gives C14H24CuN6O4 at about 403.9 g/mol, which is the uncomplexed GHK tripeptide (C14H24N6O4, ~340.4, CID 73587) plus one copper atom at ~63.5. Major suppliers list the same 403.9 figure. A smaller set of sources writes the chelate in its deprotonated form, C14H22CuN6O4 at about 401.9, which is a notation difference rather than a different substance. What is not a notation difference is a vendor quoting the bare tripeptide weight (~340.4) for a copper product - that is a genuine 63-dalton discrepancy worth questioning.
  • GLP-3 RT. The consensus figure is ~4731.3 g/mol against C221H342N46O68 (CAS 2381089-83-2, 39 residues), and it is what chemical databases and supplier technical data sheets carry. A minority of listings report ~4894.6 g/mol against a different formula (C228H350N48O66). We are not treating those as equally weighted: the lower figure has far better support, and the higher one looks like an outlier. Flag it “verify” anyway, and let the specific COA and mass trace settle it for the batch in front of you.

We have not invented a single CAS number, formula, or weight for this page. Where a value is uncertain, the table says so rather than faking precision.

Why this matters for vetting a vendor

A molecular-weight table is a vetting instrument, not trivia. Here is the chain:

  1. A legitimate COA includes a mass-spec section. Its measured mass must be consistent with the compound’s formula in the correct convention (monoisotopic). This table gives you the expected value to check against.
  2. If a vendor’s COA shows a mass that cannot be reconciled with the claimed peptide - even after accounting for salt form and average-vs-monoisotopic - you are looking at either the wrong molecule, a mislabeled document, or a template someone filled in carelessly.
  3. The COA must be independently verifiable, not a PDF the vendor emailed you. That means a named third-party lab and an accession number you can look up at the lab’s own site. A weight that matches the table but sits on an unverifiable certificate proves nothing.

For the full checklist, see how to read a peptide COA, the peptide vendor red flags list, and how to vet a US peptide vendor. A weight that matches is necessary but not sufficient; the accession-level lookup is what closes it.

How Pepora fits

We disclose up front that coaindex is a Pepora affiliate, so read this as the narrow, checkable claim it is. Pepora (peporalabs.com) ships from the US and publishes third-party COAs from Freedom Diagnostics, a US lab that runs HPLC for purity and LC-MS for identity and makes results searchable by search code at FreedomDiagnosticsTesting.com. Those accession-verifiable COAs currently exist for four SKUs: GHK-Cu at 99.98% (search code Pepo2603130126), Tesamorelin at 99.348% (Pepo2603130125), TB-500 / Thymosin Beta-4 at 99.699% (Pepo2603130123), and GLP-3 RT at 99.67% (Pepo2603130122). For those four, you can take the mass-spec section of the certificate and check it against the formulas and weights in the table above.

The honest limit: that is four SKUs, not the whole catalog. Pepora also lists BPC-157, Epitalon, Thymosin Alpha-1, ARA-290, and blend products, and for those we are not claiming a Freedom Diagnostics accession-verifiable COA - if one is not published, hold the vendor to the same standard you would hold anyone. The reason Pepora ranks well on this site is the verifiable-COA mechanism on the SKUs that have it, not blanket coverage.

The disclosed pick

Disclosure: coaindex is a Pepora affiliate and earns a commission on code SINGLES15. Pepora is scored on the same published criteria as every other supplier in our vendor table at /vendors, where it currently does not rank first.

If you want peptides whose COA you can actually verify by accession number:

Pepora publishes Freedom Diagnostics (US lab) COAs with lookup-able search codes for GHK-Cu, Tesamorelin, TB-500, and GLP-3 RT - the four SKUs where you can cross-check the mass-spec result against the molecular weights on this page. Ships from the US. Confirm the accession at the lab's own site before you trust any certificate, including these.

Check Pepora COAs at peporalabs.com

Coupon code: SINGLES15

FAQ

What is the molecular weight of BPC-157? BPC-157 free base has a molecular weight of about 1419.5 g/mol (formula C62H98N16O22, CAS 137525-51-0), a 15-amino-acid peptide. Most vendors ship the acetate salt, a separate PubChem record at about 1479.6 g/mol (C64H102N16O24), which weighs more per molecule. That is why a COA mass number can differ from the free-base figure. Verify which species the certificate reports.

Why do peptide molecular weights differ between vendors? Three reasons: salt form (free base vs acetate vs TFA salt adds counter-ions and mass), average vs monoisotopic weight (mass-spec reports monoisotopic; catalogs usually report average), and rounding. None of these mean a product is fake, but they explain why the same peptide shows two different numbers. Always compare like-for-like against the third-party COA.

What is the difference between average and monoisotopic molecular weight? Average molecular weight uses the natural isotopic abundance of every element and is what chemical catalogs list. Monoisotopic weight uses only the most abundant isotope of each element and is what a mass spectrometer measures on a COA. For small peptides the two are within a fraction of a dalton; for large ones they can diverge by several daltons.

Does salt form change the molecular weight shown on a COA? Yes. A peptide supplied as an acetate or trifluoroacetate (TFA) salt carries counter-ions that add mass. The free-base (or free-acid) molecular weight is the peptide alone. A COA may report the free-base mass by mass spec while the vial is filled as salt, which is one reason net peptide content can be lower than gross vial weight.

What is the molecular weight of GLP-3 RT? The weight of evidence points to about 4731.3 g/mol for formula C221H342N46O68 (CAS 2381089-83-2), a 39-residue peptide, and that figure is consistent across chemical databases and supplier technical data sheets. A minority of listings instead report about 4894.6 g/mol against a different formula (C228H350N48O66). Treat the higher figure as an outlier rather than an equal alternative, and confirm the number against the specific vendor COA and mass-spec trace before relying on it.

How is molecular weight used in reconstitution or cost-per-mg math? Molecular weight is not needed to reconstitute by milligrams; that math uses only the labeled peptide mass and the solvent volume. MW matters when converting between milligrams and molar concentration in research models. For practical mg-to-mL math, use a reconstitution calculator and a cost-per-mg calculator, and use MW only when a protocol is written in molar terms. This is research context, not a dosing instruction.

References

  1. PubChem, BPC-157 (CID 9941957), C62H98N16O22, MW 1419.5; BPC-157 acetate (CID 155977614), C64H102N16O24, MW 1479.6. https://pubchem.ncbi.nlm.nih.gov/compound/9941957
  2. PubChem, timbetasin / thymosin beta-4 (TB-500) (CID 16132341), C212H350N56O78S, MW ~4963. https://pubchem.ncbi.nlm.nih.gov/compound/16132341
  3. PubChem, Cu-GHK / copper tripeptide-1 (CID 378611), C14H24CuN6O4, MW 403.9; uncomplexed GHK (CID 73587), C14H24N6O4, MW 340.4. https://pubchem.ncbi.nlm.nih.gov/compound/378611
  4. DrugBank, Tesamorelin (DB08869), C221H366N72O67S, MW 5135.76; PubChem CID 16137828. https://go.drugbank.com/drugs/DB08869
  5. PubChem, Epitalon (CID 219042), C14H22N4O9, MW 390.35. https://pubchem.ncbi.nlm.nih.gov/compound/219042
  6. PubChem, thymalfasin / thymosin alpha-1 (CID 16130571), C129H215N33O55, MW 3108.3. https://pubchem.ncbi.nlm.nih.gov/compound/16130571
  7. PubChem, cibinetide / ARA-290 (CID 91810664), C51H84N16O21, MW 1257.3. https://pubchem.ncbi.nlm.nih.gov/compound/91810664
  8. GLP-class research peptide, CAS 2381089-83-2, C221H342N46O68, MW 4731.33 - consensus value across chemical databases and supplier data sheets; a minority of secondary listings report ~4894.6 against a different formula. Verify against the product-specific COA. https://www.chemicalbook.com/ChemicalProductProperty_EN_CB912574543.htm
  9. Freedom Diagnostics Testing - search-code lookup for third-party COAs. https://freedomdiagnosticstesting.com/search-for-your-coa-based-on-the-unique-accession-number/

coaindex is a Pepora affiliate (peporalabs.com) and earns a commission on purchases made with the code above. This is affiliate education, not journalism, and it ranks vendors on checkable, independently verifiable third-party-COA criteria. Research use only. Not for human or veterinary use, and nothing here is medical advice.