Protein Concentration Calculator

Accurate Protein Quantification Tool

Calculate protein concentration using multiple methods: A280, Bradford, BCA, and Lowry. Enter your data and get instant, reliable results for your laboratory needs.

Example Calculations

Try these sample data sets to see how the calculator works

A280 Direct Measurement

A280 Direct Measurement

Calculate protein concentration using A280 absorbance for BSA.

Method: A280 (UV Absorbance)

Absorbance (A280): 0.85

Extinction Coefficient: 43824 M⁻¹cm⁻¹

Molecular Weight: 66000 Da

Dilution Factor: 1

Path Length: 1 cm

Bradford Assay with Standard Curve

Bradford Assay with Standard Curve

Determine protein concentration using Bradford assay and standard curve.

Method: Bradford Assay

Standard Absorbances: 0.05, 0.12, 0.21, 0.32

Standard Concentrations: 0.1, 0.2, 0.4, 0.8 mgml

Sample Absorbance: 0.27

BCA Assay Example

BCA Assay Example

Protein quantification using BCA assay and standard curve.

Method: BCA Assay

Standard Absorbances: 0.04, 0.11, 0.19, 0.29

Standard Concentrations: 0.1, 0.25, 0.5, 1.0 mgml

Sample Absorbance: 0.22

Lowry Assay Example

Lowry Assay Example

Protein concentration calculation using Lowry assay.

Method: Lowry Assay

Standard Absorbances: 0.06, 0.13, 0.22, 0.35

Standard Concentrations: 0.2, 0.4, 0.8, 1.6 mgml

Sample Absorbance: 0.28

Other Titles
Understanding Protein Concentration: A Comprehensive Guide
Master protein quantification with multiple methods and best practices

What is Protein Concentration?

  • Definition and Importance
  • Measurement Methods
  • Applications in Research
Protein concentration refers to the amount of protein present in a solution, typically expressed in mg/mL or μg/μL. Accurate quantification is essential for biochemical experiments, protein purification, and enzyme assays.
Why Measure Protein Concentration?
Knowing the exact protein concentration ensures reproducibility and reliability in research, diagnostics, and industrial applications. It is a critical parameter in molecular biology, biochemistry, and biotechnology.
Common Measurement Methods
The most common methods include A280 absorbance (for pure proteins), and colorimetric assays such as Bradford, BCA, and Lowry, which require a standard curve for quantification.

Measurement Examples

  • A280 for purified BSA
  • Bradford assay for cell lysate
  • BCA for enzyme preparations

Step-by-Step Guide to Using the Protein Concentration Calculator

  • Select Method
  • Enter Data
  • Interpret Results
Our calculator supports four major protein quantification methods. Select the appropriate method based on your sample type and available data.
A280 Method
For pure proteins, enter absorbance at 280 nm, extinction coefficient, molecular weight, dilution factor, and path length. The calculator uses Beer-Lambert law for direct quantification.
Colorimetric Assays (Bradford, BCA, Lowry)
For these assays, enter standard absorbances and concentrations, and the absorbance of your unknown sample. The calculator fits a linear regression to the standards and calculates the sample concentration.
Result Interpretation
The result includes protein concentration, standard curve equation, and R² value for curve fit quality. Use these to assess the reliability of your quantification.

Usage Examples

  • A280: Direct calculation for BSA
  • Bradford: Standard curve for cell lysate
  • BCA: High sensitivity for dilute samples

Real-World Applications of Protein Concentration Calculations

  • Protein Purification
  • Enzyme Kinetics
  • Diagnostics
Protein quantification is vital in protein purification workflows, enzyme activity assays, and diagnostic tests. Accurate measurement ensures correct reagent preparation and experimental reproducibility.
Protein Purification
During purification, protein concentration is monitored to assess yield and purity. The calculator helps track these parameters at each step.
Enzyme Kinetics
Enzyme assays require precise protein quantification to determine specific activity and kinetic parameters.
Clinical Diagnostics
Diagnostic tests often rely on protein quantification, such as albumin in blood or urine. Reliable results are essential for patient care.

Application Examples

  • Affinity purification monitoring
  • Enzyme activity normalization
  • Albumin quantification in diagnostics

Common Misconceptions and Correct Methods

  • A280 Limitations
  • Standard Curve Pitfalls
  • Sample Preparation Errors
Misconceptions in protein quantification can lead to inaccurate results. Understanding method limitations and best practices is crucial.
A280 is Only for Pure Proteins
A280 method is accurate only for pure proteins without interfering substances. Contaminants like nucleic acids or detergents can skew results.
Standard Curve Must Be Linear
Ensure your standards cover the expected sample range and the curve is linear. Outliers or non-linear regions reduce accuracy.
Dilution Errors
Always account for dilution factors and use precise pipetting. Small errors can significantly affect final concentration values.

Best Practice Guidelines

  • Avoid A280 for crude lysates
  • Check R² for standard curve
  • Use fresh standards for each assay

Mathematical Derivation and Examples

  • Beer-Lambert Law
  • Linear Regression for Standard Curves
  • Error Analysis
Protein quantification relies on established mathematical principles. Understanding these helps troubleshoot and optimize your experiments.
Beer-Lambert Law (A280)
C = (A × DF × MW) / (ε × l), where C is concentration (mg/mL), A is absorbance, DF is dilution factor, MW is molecular weight, ε is extinction coefficient, and l is path length (cm).
Linear Regression for Standard Curves
For colorimetric assays, a standard curve is generated by plotting absorbance vs. concentration. Linear regression yields the equation y = mx + b, used to calculate unknown concentrations.
Assessing Curve Fit
R² value indicates the goodness of fit. Values close to 1.0 indicate a reliable standard curve.

Calculation Examples

  • A280: C = (0.85 × 1 × 66000) / (43824 × 1) = 1.28 mg/mL
  • Bradford: y = 1.02x + 0.03, sample A = 0.27, C = (0.27-0.03)/1.02 = 0.24 mg/mL
  • BCA: R² = 0.998 indicates excellent fit