Peptide Property Calculator
Enter one peptide sequence to get its average and monoisotopic neutral mass, elemental formula, net charge at your selected pH, theoretical pI, Kyte–Doolittle GRAVY and estimated ε280 in one place. Each result is a theoretical prediction, shown with its method and a plain-language note. Try the example sequence ACDWYK to see how the results work. For laboratory research use only.
Sequence results
Enter your sequence or try the example to see its theoretical properties.
- Average neutral mass
- Monoisotopic neutral mass
- Net charge at pH
- Theoretical pI
- GRAVY
- Estimated ε280 (M⁻¹ cm⁻¹)
No tryptophan or tyrosine. This model cannot provide a usable ε280 for calculating concentration.
Same sequence, same pH
- Monoisotopic mass
- Mass change
- Net charge
- Theoretical pI
Formula · Residues
One-letter
Three-letter
Explore the sequence
Select a residue to see its contribution. Use arrow keys or swipe to move along the chain.
- Modeled side-chain charge
- Hydropathy score
- ε280 contribution (M⁻¹ cm⁻¹)
How the calculator works
This peptide sequence calculator accepts one-letter code, a single FASTA sequence, or separated three-letter code for the 20 standard amino acids, from 1 to 500 residues. It models a linear backbone with a free or N-acetyl N-terminus and a free or C-amide C-terminus, with cysteine treated as reduced. Disulfide bonds, other modifications, cyclic peptides and nonstandard residues fall outside this combined model. The Molecular Weight Calculator handles some of these for mass. Your sequence also appears in normalized three-letter notation, and you can copy a summary of the results.
| Property | Calculation basis |
|---|---|
| Mass and formula | The calculator reports the formula and neutral masses in daltons. These values are built from residue masses (UW Proteomics Resource) and elemental masses (Unimod). Water is added for free termini, and the acetyl or amide cap changes are applied separately. Average mass uses isotope-weighted atomic masses. Monoisotopic mass uses the most abundant isotope of each element. |
| Net charge and pI | Net charge uses the IPC peptide pKa set (Kozlowski) at any pH from 0 to 14. You can set the pH with the slider or type an exact value. The plot shows charge against pH with a zero line. The pI is the point where the modeled curve crosses zero, and the plot marks it. If the curve has no crossing or no unique pI, the result says so. Terminal settings affect both charge and pI. |
| GRAVY | GRAVY is the arithmetic mean of the Kyte–Doolittle hydropathy values for each residue (ExPASy ProtScale). It describes the sequence only. It does not include cap or solvent effects, and it does not predict solubility. |
| Estimated ε280 | For this reduced model, ε280 = 5500 × Trp + 1490 × Tyr, in M⁻¹ cm⁻¹ (ExPASy ProtParam, Pace method). This value is an estimate from the sequence. It is not a measured A280. |
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Check the listing and match your lot documentation before comparing calculated properties.
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Peptide property calculator FAQs
Should I use average or monoisotopic mass?
Use the same mass convention as the analytical result you are comparing against. These are theoretical neutral masses, not an observed spectrum, so they cannot explain which peaks appear in your data.
How do I find the pI of my peptide?
Find the point where the modeled charge curve crosses zero. Then check that the IPC peptide model and your selected end forms match your peptide.
Can GRAVY tell me whether my peptide will dissolve?
No. GRAVY is a sequence average only. Test solubility in your actual medium and conditions. Bachem's peptide solubility guide is a useful starting point.
Why is my ε280 estimate zero or low?
In this model, only Trp and Tyr contribute to ε280. A sequence with neither residue scores zero, so you cannot use the estimate to infer concentration. To find concentration, measure A280 and apply the path length and blank correction in the measured A280 tool.
Can these predictions confirm my batch identity?
No. Calculator results are theoretical. To check identity, use the original report for that lot, and compare on the same basis the report uses, such as a measured ion (m/z) or a neutral mass. You can find lot reports in COA Finder.
