What is the Bradford assay?

The Bradford assay is a colorimetric method for measuring total protein concentration. Coomassie Brilliant Blue G-250 dye binds to proteins and shifts its absorbance maximum to 595 nm; the color intensity is proportional to protein concentration.

What standard protein is typically used?

Bovine Serum Albumin (BSA) is the most common standard. A typical working range is 0–2000 µg/mL for the standard Bradford assay or 0–25 µg/mL for the micro-Bradford format.

What R² value is acceptable?

An R² of 0.99 or higher indicates a reliable standard curve. Values below 0.98 suggest pipetting errors, reagent degradation, or non-linearity at the extremes of the range.

Why should I dilute my sample?

Accurate interpolation only works within the linear range of the standard curve. If your sample absorbance falls outside the highest standard point, dilute it and re-measure, then multiply the result by the dilution factor.

Does the Bradford assay work for all proteins?

Response varies by protein because the dye binds arginine and hydrophobic residues differently. BSA is the conventional standard; some labs use IgG. Results are comparative, not absolute, unless your standard matches your target protein.

Protein Concentration Bradford

Enter BSA standard absorbance values and your unknown sample absorbance to calculate protein concentration via linear regression.

BSA Standard Curve

Enter concentration (µg/mL) and absorbance (A₅₉₅) for each standard point. Add at least 3 points.

Sample absorbance (A₅₉₅)

Sample dilution factor (if diluted before assay)

Load example data

Regression & Result

Enter standard points and sample absorbance, then click Calculate.

Standard Curve Data

Conc. (µg/mL)	Absorbance	Predicted A	Residual
No data yet

Summary

Enter BSA standard absorbance values and your unknown sample absorbance to calculate protein concentration via linear regression.

How it works

Enter at least 3 BSA standard points (concentration in µg/mL and absorbance at 595 nm).
The tool fits a linear regression line through the standard data.
Enter your unknown sample absorbance value.
The calculator solves for concentration using the regression equation.
View R² to assess standard curve quality; values above 0.99 are typical for a good assay.

Use cases

Quantify total protein before SDS-PAGE or Western blot.
Normalize protein loading across multiple samples.
Verify protein yield after purification.
Quality-check a new Bradford reagent batch with known standards.
Compare protein content between cell lysates.
Determine sample dilution needed to hit a target concentration.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu