Peptide calculator
Choose a profile from the collection or enter a one-letter amino acid sequence. Explore a linear, unmodified sequence model: molecular weight, formula, estimated isoelectric point and charge at any pH. Free, instant, and calculations stay in your browser.
Explore the full collection
Browse collection profiles by name. A sequence model is offered only when a compatible reference sequence is available; other entries link to their profiles without inventing missing chemistry.
106 profiles · 34 reference sequence models · 72 profile-only entries
Reference sequences come from the published VALREXA profiles and are not independently re-verified by this calculator. A calculated result does not establish a compound's identity, effectiveness or safety.
Choose a profile above, or enter a custom sequence below. Results always use a linear, unmodified reference model.
Read the collection profileProperties
- Molecular formula
- GRAVY (hydropathy)
- Extinction coefficient
Net charge vs. pH
Dashed line: isoelectric point. Dot: your selected pH.
Sequence map
Composition
| Count | % |
|---|
How it's calculated
- Assumes a linear peptide of the 20 standard amino acids with a free N-terminus (–NH₂) and C-terminus (–COOH). Modifications such as amidation, acetylation, D-amino acids or salts are not included.
- Molecular weight uses average isotopic masses (sum of residue masses plus one water). It is a calculated reference value, not a measurement, and does not include salts or product-specific modifications.
- Charge and pI use the Henderson–Hasselbalch equation with EMBOSS pKa values: N-terminus 8.6, C-terminus 3.6, Asp 3.9, Glu 4.1, His 6.5, Cys 8.5, Tyr 10.1, Lys 10.8, Arg 12.5. Different pKa sets give slightly different pI values.
- Extinction coefficient at 280 nm: Trp 5,500, Tyr 1,490 and cystine 125 M⁻¹cm⁻¹ (Pace et al., 1995). GRAVY is the mean Kyte–Doolittle hydropathy (1982).
For teaching and sequence exploration, not treatment or dosing decisions. Experimental values can differ.
VALREXA Biosciences. (2026, November 7). Peptide calculator: molecular weight, pI and net charge. VALREXA Biosciences. https://valrexa.com/calculator.html
APA style · Last reviewed November 7, 2026 · Our editorial standards