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Research-use sequence analysis

Peptide Property & Solubility Calculator

Enter a peptide sequence to calculate molecular weight, net charge, theoretical pI, GRAVY hydrophobicity and sequence-based solubility guidance for laboratory research.

One sequence. Multiple research properties.
Mass
MW & formula
Charge
Net charge & pI
Hydropathy
GRAVY & hydrophobic %
Handling
Solvent guidance

Analyze your peptide sequence

Supports the 20 standard amino acids using one-letter codes. Calculations assume an unmodified linear peptide with free N- and C-termini.

Spaces, line breaks and hyphens are ignored.

What does this peptide calculator calculate?

The calculator translates a standard one-letter peptide sequence into physicochemical properties that help researchers assess identity, charge behavior, hydrophobicity and practical solubilization strategy.

Molecular weight & formula

Average molecular weight and monoisotopic mass are calculated for an unmodified linear peptide with free termini. The molecular formula is derived from the sequence after peptide-bond water loss.

Net charge & theoretical pI

Charge is estimated at the selected pH with standard pKa values and the Henderson–Hasselbalch relationship. The pI is the estimated pH where net charge approaches zero.

GRAVY & hydrophobicity

GRAVY is the mean Kyte–Doolittle hydropathy value across the sequence. Positive values indicate a more hydrophobic overall sequence; negative values indicate a more hydrophilic tendency.

Solubility & solvent guidance

The recommendation combines sequence length, calculated charge, hydrophobic-residue content and proximity to the theoretical pI to suggest a sensible starting strategy—not an exact solubility concentration.

How to interpret peptide solubility guidance

Peptide solubility cannot be determined from sequence alone. However, charge and hydrophobicity provide useful starting information for solvent selection and small-scale solubility testing.

JPT recommends testing a small quantity first. Positively charged peptides can often be approached with water or buffer followed, if needed, by acidic conditions; negatively charged peptides can be approached with water or buffer followed by basic conditions. Uncharged, strongly hydrophobic sequences may require an organic co-solvent.

Sequence signal
Practical interpretation
Positive charge
Try water/buffer first; consider lowering pH if needed.
Negative charge
Try water/buffer first; consider raising pH if needed.
Near theoretical pI
Net charge is minimized and solubility may decrease.
Neutral + >25% hydrophobic residues
Consider a small amount of organic solvent before aqueous dilution.
For detailed solvent steps, DMSO/DMF precautions and troubleshooting, use JPT's dedicated peptide solubilization guide. This calculator intentionally does not duplicate that protocol.

Methodology & limitations

Sequence scope

Version 1 supports the 20 standard amino acids and assumes free N- and C-termini. It does not calculate the mass or charge effects of labels, protecting groups, terminal modifications, non-standard residues or counterions.

Charge & pI

Ionizable groups are modeled with standard approximate pKa values. Local sequence environment can shift real pKa values, so calculated charge and pI should be treated as estimates.

Hydropathy

GRAVY is calculated as the arithmetic mean of Kyte–Doolittle hydropathy values. It describes sequence hydropathy; it is not a direct measurement of peptide solubility.

Experimental confirmation

Concentration, buffer, temperature, salt form, aggregation and modifications can change real behavior. For measured solubility or additional analytics, use JPT's peptide analysis services.

Peptide calculator FAQ

What is a peptide calculator?
A peptide calculator converts an amino-acid sequence into estimated physicochemical properties such as molecular weight, net charge, theoretical isoelectric point and hydrophobicity. A research-focused calculator can also use those properties to support decisions about peptide handling and solubilization.
Can peptide solubility be calculated exactly from a sequence?
No. Sequence-based properties can indicate whether a peptide is charged or hydrophobic and help select a starting solvent strategy, but real solubility also depends on concentration, pH, buffer composition, temperature, salt form, aggregation, modifications and experimental conditions. Solubility should be confirmed experimentally.
How is peptide molecular weight calculated?
For an unmodified linear peptide, the calculator sums residue masses and adds the mass of one water molecule, corresponding to free N- and C-termini. The displayed value does not include counterions, labels or other modifications.
How is peptide net charge calculated?
The calculator estimates the protonation state of the N-terminus, C-terminus and ionizable side chains at the selected pH using standard approximate pKa values and the Henderson–Hasselbalch relationship. The individual contributions are then summed to estimate net charge.
What does the theoretical pI of a peptide mean?
The theoretical isoelectric point (pI) is the estimated pH at which the peptide's net charge is approximately zero. Solubility can decrease near the pI because electrostatic repulsion is reduced, although the magnitude of this effect depends on the specific sequence and conditions.
What is GRAVY in a peptide sequence?
GRAVY means Grand Average of Hydropathy. It is the average hydropathy value across all residues in the sequence. More positive values indicate a more hydrophobic overall sequence, while more negative values indicate a more hydrophilic tendency.
What solvent should I use to dissolve a peptide?
Start with a small amount. Water or buffer is often the first choice for charged peptides. If needed, basic peptides may benefit from more acidic conditions and acidic peptides from more basic conditions. Uncharged, hydrophobic peptides may require a small amount of organic solvent before stepwise aqueous dilution. Follow JPT's dedicated solubilization protocol for detailed guidance.
Does the calculator support modified or non-standard amino acids?
Not in this version. The calculator accepts the 20 standard one-letter amino-acid codes. Modified termini, labels, non-standard residues, cyclization, disulfides and counterions require separate mass and charge handling.

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