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Protein Concentration (BCA / Bradford) Calculator

Calculate protein concentration from spectrophotometric assay absorbance using a BSA standard curve slope and intercept.

Absorbance of unknown sample at the assay wavelength (562 nm for BCA, 595 nm for Bradford).
Absorbance of blank control (reagent without protein).
Slope from BSA standard curve linear regression (Absorbance per ug/mL).
Y-intercept from standard curve linear regression.
Dilution factor applied to sample before assay (1 = undiluted).

Results

Protein Concentration (actual)175.00 ug/mL protein
Corrected Absorbance0.400 AU corrected

📖What is it?

The BCA (bicinchoninic acid) and Bradford assays measure protein concentration colorimetrically by comparing sample absorbance against a BSA (bovine serum albumin) standard curve. This calculator extracts concentration from the linear equation: Abs = slope x [protein] + intercept.

🎯How to use

Run your standard curve assay with BSA standards, fit a linear trendline (e.g. in Excel or GraphPad), and note the slope and intercept. Enter the blank-subtracted absorbance of your unknown and the slope/intercept from your curve. If your sample was diluted before the assay, enter the dilution factor to get the true concentration.

💡Example scenario

Standard curve: slope = 0.002 AU/(ug/mL), intercept = 0.05. Unknown absorbance = 0.45, blank = 0.05. Corrected Abs = 0.40. Concentration from curve = (0.40 - 0.05) / 0.002 = 175 ug/mL. If sample was diluted 5-fold, actual = 875 ug/mL.

🏆Pro tip

BCA is more sensitive (1-2000 ug/mL) and compatible with reducing agents if used at low temperature. Bradford is faster but incompatible with detergents >0.1% SDS. NanoDrop (A280) is best for pure proteins (extinction coefficient-based). For crude lysates, always use a wet chemical assay (BCA/Bradford) over NanoDrop since nucleic acids absorb at 280 nm too.