Calculate molecular weight, isoelectric point, extinction coefficient, amino acid composition, and GRAVY score from a protein sequence. Data never leaves your browser.
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Glycoproteins, membrane proteins, and highly charged proteins can migrate anomalously on SDS-PAGE. A 10-20% deviation from calculated MW is not uncommon for these protein classes.
Calculated pI assumes isolated, unfolded protein in dilute solution. Actual pI can shift ±0.5 units due to ionic strength, nearby charged residues in the folded structure, and post-translational modifications.
Proteins lacking Trp and Tyr residues have essentially zero absorbance at 280nm. For these proteins, use A205 or colorimetric assays (Bradford, BCA) for concentration measurement.
If your expression construct includes an N-terminal signal peptide, His-tag, or fusion partner, include those residues for accurate MW. For secreted proteins, remove the signal peptide sequence.
MW from NIST residue masses + water. pI via bisection on Henderson-Hasselbalch net charge equation (standard pKa set). Extinction via Pace method (Trp 5500, Tyr 1490, Cys-Cys 125). GRAVY via Kyte-Doolittle scale.
Last validated 2026-04-05. Calculations are designed for planning and documentation support; verify procurement decisions against manufacturer specifications or institutional SOPs.
ConductScience Protein MW & pI Calculator (v1.0). ConductScience, Inc. 2026. Available at: https://conductscience.com/tools/protein-mw-calculator
Pace CN, et al. How to measure and predict the molar absorption coefficient of a protein. Protein Sci. 1995;4(11):2411-2423. doi:10.1002/pro.5560041120
Every protein has physical properties determined by its amino acid sequence:
• Molecular weight: Sum of residue masses + water. Critical for SDS-PAGE interpretation, Western blot ladder selection, and mass spec identification • Isoelectric point (pI): pH of zero net charge. Determines migration in isoelectric focusing, solubility minimum, and optimal ion exchange chromatography conditions • Extinction coefficient (ε₂₈₀): Enables concentration measurement by UV absorbance using Beer-Lambert law: c = A₂₈₀/ε • GRAVY score: Predicts solubility and membrane association tendency
Common uses for these calculations:
• SDS-PAGE: Compare calculated MW with observed migration to detect PTMs, cleavage, or aggregation • Protein purification: Choose ion exchange resin based on pI (anion exchange for pI < buffer pH, cation for pI > buffer pH) • Concentration measurement: Use ε₂₈₀ with A₂₈₀ reading to calculate concentration without Bradford/BCA assays • Expression construct design: Verify expected MW of fusion proteins, tagged constructs, and truncations
