Protein Concentration Calculator
Calculate corrected absorbance and diluted and original protein concentrations based on sample absorbance, blank absorbance, extinction coefficient, path length, dilution factor, and molecular weight. Protein Concentration Calculator supports researchers, laboratory technicians, and students quantifying protein samples by spectrophotometry.
Highlights
- Corrects sample absorbance by subtracting blank absorbance.
- Calculates diluted and original protein molar concentrations.
- Converts protein concentration into convenient mass-based units.
- Accounts for extinction coefficient and optical path length.
- Applies dilution factors for accurate original sample results.
Table of Contents
How Protein Concentration Calculator Works?
The Protein Concentration Calculator uses spectrophotometric absorbance measurements and the Beer–Lambert law to estimate protein concentration. First, the blank signal from the buffer or reagent is subtracted from the measured sample absorbance:
The corrected absorbance is then used in the Beer–Lambert relationship. The diluted molar concentration is calculated from the corrected absorbance, molar extinction coefficient, and optical path length:
Here, c is the protein concentration in molar units, ε is the protein-specific molar extinction coefficient, and l is the optical path length. The original sample concentration is obtained by applying the entered dilution factor:
To calculate mass-based concentration, the molar concentration is multiplied by the protein molecular weight:
The calculator reports corrected absorbance, diluted and original molar concentration, and diluted and original mass concentration. Supported output formats include M, mM, µM, mg/mL, g/L, µg/mL, and µg/µL.
| Calculation stage | Formula or input | Result |
|---|---|---|
| Blank correction | Sample absorbance − blank absorbance | Corrected absorbance |
| Diluted molar concentration | Corrected absorbance ÷ (extinction coefficient × path length) | Concentration of measured sample |
| Original molar concentration | Diluted concentration × dilution factor | Concentration before dilution |
| Mass concentration | Molar concentration × molecular weight | Protein concentration by mass |
For example, using the default values gives a corrected absorbance of 0.60 AU. With an extinction coefficient of 43,800 M−1 cm−1 and a 1 cm path length, the diluted concentration is approximately 1.37 × 10−5 M. A dilution factor of 10 gives an original concentration of approximately 1.37 × 10−4 M.
Practical Use Cases
Biomedical and molecular biology researchers: Researchers can estimate the concentration of purified proteins before enzyme assays, binding experiments, structural studies, or sample loading. Entering the measured absorbance, protein-specific extinction coefficient, path length, dilution factor, and molecular weight provides both molar and mass-based results.
Laboratory technicians: Technicians can use the calculator to correct readings for buffer or reagent background and report the concentration of the original sample rather than only the diluted measurement. This is useful for quality-control records, batch testing, and preparation of working protein solutions.
Biochemistry students: Students can use the calculator to connect blank correction with the Beer–Lambert law and observe how extinction coefficient, optical path length, and dilution factor affect the final concentration. The separate diluted and original outputs make each calculation step easier to check.
Protein purification specialists: Purification teams can estimate protein concentration in collected fractions and compare samples with different dilution factors. Mass-based outputs can support pooling decisions and preparation of downstream chromatography, electrophoresis, or assay samples.
Accuracy and Limitations
The calculation is mathematically accurate when the blank absorbance, extinction coefficient, path length, dilution factor, molecular weight, and sample absorbance are correct and the sample follows Beer–Lambert behavior. Accuracy is limited by pipetting and dilution errors, incorrect protein-specific extinction coefficients, inaccurate path-length settings, wavelength mismatch, turbidity, light scattering, reagent interference, and detector nonlinearity. A blank absorbance greater than the sample absorbance produces a negative corrected absorbance, which is generally not a meaningful protein concentration. Absorbance values near the upper end of the supported 0–5 AU input range may also be less reliable if the instrument is outside its linear measurement range. The calculator does not correct for aggregation, overlapping absorbing compounds, or deviations from the assumed extinction coefficient.
Quick Examples
Example #1: Standard Protein Assay
Quantify a moderately concentrated protein sample using a 1 cm cuvette and a 10-fold dilution.
Example #2: Microplate Protein Measurement
Determine protein concentration from a microplate reading using a short optical path length and a higher dilution factor.
Example #3: Low-Concentration Protein Sample
Estimate the concentration of a dilute protein sample with minimal dilution using a standard cuvette.
