Bradford Assay Protein Concentration Calculator
Build a BSA standard curve from your absorbance readings, get the linear fit and R², and convert sample absorbances into protein concentrations with dilution factors.
How it works
Least-squares fit A = m·C + b on the standards; C_sample = (A − b) ÷ m × dilution factor
The Bradford (Coomassie) assay turns blue in proportion to protein, but only linearly over a limited range (roughly 100–1,000 µg/mL for the standard assay, 1–25 µg/mL for the micro assay). Fit the standards, check R², and only read samples that fall inside the curve — anything above the top standard must be diluted and re-read. Bradford responds mostly to arginine and aromatic residues, so BSA standards overestimate some proteins; use the same protein as a standard when accuracy matters.
Worked example
Six BSA standards give A = 8.5×10⁻⁴·C + 0.003 (R² 0.999). A sample reading 0.312 is 363 µg/mL in the cuvette — 3.63 mg/mL of stock after the 1:10 dilution.
Frequently asked questions
Should the blank be subtracted?
Include the 0 standard in the fit and its absorbance becomes the intercept; do not subtract twice.
Why is my curve flattening at the top?
Dye saturation — drop the top standards or move to a diluted sample so readings stay below about 1.0.
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For teaching and planning — verify against your lab protocol and instrument documentation.