GRAVY

How to calculate a GRAVY score

Paste a protein sequence, either as plain one-letter amino acid text or in FASTA format, and run the calculator. ProteinIQ averages the Kyte-Doolittle hydropathy value across every residue and returns a three-decimal GRAVY (Grand Average of Hydropathy) score for each sequence. Use it as a compact description of overall protein hydrophobicity, not as a position-by-position membrane-topology prediction.

For example, this short sequence contains three strongly hydrophobic residues:

>AIV_reference
AIV

It returns a GRAVY score of 3.500, because (1.8 + 4.5 + 4.2) / 3 = 3.5.

The calculator also accepts several FASTA records in one submission. This input:

>AIV_reference
AIV
>charged_peptide
DEKR

returns these rows:

The protein ID is the first space- or pipe-delimited token in a FASTA header. For example, >sp|P12345|NAME description is displayed as sp.

Input

The tool rejects a sequence containing a noncanonical residue such as B, J, O, U, X, or Z. Before validation, the FASTA parser removes non-letter characters from sequence lines, so whitespace, digits, alignment gaps, and punctuation do not contribute residues or score values. Check an alignment-derived sequence before interpreting its length or score.

Settings

GRAVY has no user-configurable settings. It always uses the Kyte-Doolittle hydropathy scale and rounds the displayed score to three decimal places.

Results

The results table can be copied or downloaded for batch comparisons.

What does a GRAVY score mean?

GRAVY is calculated as:

Here, $N$ is the number of residues and $h_i$ is the Kyte-Doolittle hydropathy value assigned to residue $i$. Isoleucine (I, 4.5), valine (V, 4.2), leucine (L, 3.8), and phenylalanine (F, 2.8) raise the average. Charged residues such as arginine (R, -4.5), lysine (K, -3.9), aspartate (D, -3.5), and glutamate (E, -3.5) lower it.

A positive score means hydrophobic residues outweigh hydrophilic ones on this scale. A negative score means the reverse. The sign is more reliable than a universal cutoff: protein length, domain composition, oligomerization, disulfides, cofactors, and experimental conditions all affect real solubility and localization. A positive whole-protein average can support a membrane-association hypothesis, but it does not identify a transmembrane segment or establish that a protein is insoluble.

GRAVY also cannot distinguish where hydrophobic residues occur. A sequence with a short hydrophobic helix and a polar soluble domain can have a modest global score. Use a hydropathy plot to inspect the local pattern along the sequence.

Which protein property tool should I use?

FAQ

Is GRAVY the same as a hydropathy plot?

No. GRAVY is one average over the complete sequence. A hydropathy plot keeps positional information by calculating local averages, which makes it more useful for inspecting candidate membrane-spanning segments.

Does a positive GRAVY score prove that a protein is membrane-bound?

No. It shows that the sequence is hydrophobic on average according to the Kyte-Doolittle scale. Confirming membrane association requires local sequence context and, where appropriate, structural or experimental evidence.

Why was my protein sequence rejected?

The GRAVY workflow validates the 20 canonical amino acid letters after cleanup. Replace or remove ambiguity codes, modified-residue symbols, stop markers, and nonprotein text before submitting.

Can I calculate GRAVY for multiple FASTA sequences?

Yes. Include each sequence as a separate FASTA record. The result table contains one row per validated sequence, with its identifier, length, and GRAVY score.