Protein Parameters Calculator: MW, pI, extinction coefficient & GRAVY from sequence

Protein properties from a sequence

Paste a protein and get the numbers you reach for constantly — molecular weight, theoretical pI, the 280 nm extinction coefficient (for measuring concentration by absorbance), hydropathy, and composition — all in the browser, no account.

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What it computes

• Molecular weight — sum of average residue masses + water.
• Theoretical pI — net-charge = 0 by bisection (EMBOSS pKa set).
• Extinction coefficient (280 nm) — Pace method, reported both reduced and with all cysteines paired, plus the A₂₈₀ 0.1% (1 g/L) value for converting absorbance to concentration.
• GRAVY (grand average of hydropathy) and aliphatic index.
• Charge — acidic/basic residue counts and net charge at pH 7.
• Net-charge-vs-pH curve with the pI marked, and the amino-acid composition as a bar chart.

Accuracy

Validated against hen egg-white lysozyme (129 aa): MW 14,313.1 Da, ε 37,470 / 37,970 M⁻¹cm⁻¹, GRAVY −0.472 — exact matches to ExPASy ProtParam. The pI (9.21) differs from ProtParam’s 9.32 only because we use the EMBOSS pKa set rather than Bjellqvist; pI always varies by ~0.1–0.3 between pKa schemes.

The instability index is not included — it requires the 400-value Guruprasad dipeptide matrix, which we’d rather add from a verified source than approximate.

Embed it on your site

<link rel="stylesheet" href="https://www.37degrees.io/interactive-tools/protein-parameters/styles.css" />

<div id="protein-widget-embed"></div>

<script>
  // Optional: window.PROTEIN_THEME = "light";
</script>
<script src="https://www.37degrees.io/interactive-tools/protein-parameters/widget.js"></script>

Credits

Built and maintained by 37degrees. Average masses, EMBOSS pKa, Pace extinction coefficient, Kyte-Doolittle hydropathy — no third-party libraries, no data leaves the browser.