Protein Concentration Calculator: Fast, Accurate Protein Quantification Online
Free Protein Concentration Calculator to instantly compute protein levels using absorbance, dilution factor, path length, and extinction coefficient. Accurate and easy.
ε₂₈₀: 43,824 M⁻¹cm⁻¹
MW: 66,500 Da
Spectrophotometer reading
cm (standard cuvette = 1.0)
No dilution = 1, 1:10 dilution = 10
Formula (Beer-Lambert Law):
Molarity (M) = A / (ε × l)
Concentration (mg/mL) = M × MW / 1000
Original Concentration = Concentration × Dilution Factor
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Introduction: What This Protein Concentration Calculator Does and Who It's For
Protein concentration is one of the most common and essential measurements in biochemistry, molecular biology, biotechnology, and laboratory research. Whether you are preparing a sample for SDS-PAGE, setting up enzyme reactions, quantifying antibodies, or performing protein purification, you need to know how much protein is present in your solution.
Our **Protein Concentration Calculator** helps you determine the concentration of proteins quickly and accurately using absorbance readings, dilution information, and basic protein properties like molecular weight and extinction coefficient. This calculator is designed for students, researchers, laboratory technicians, educators, biotechnology professionals, and anyone working with protein samples worldwide.
Instead of performing manual Beer–Lambert calculations every time, this tool automates the process and minimizes errors, making your workflow faster, easier, and more reliable.
Example Scenarios and Case Studies
Below are practical examples that reflect common lab situations. These demonstrate how the calculator works step-by-step.
Example 1: BSA Quantification at 280 nm
A student measures the absorbance of a BSA solution:
- Absorbance at 280 nm: 0.75
- Dilution factor: 1 (undiluted)
- Path length: 1 cm
- Extinction coefficient (ε): 43,824 M⁻¹cm⁻¹
- Molecular weight: 66,500 Da
Using the Beer–Lambert law:
Concentration (M) = A / (ε × l) = 0.75 / (43824 × 1) ≈ 1.71 × 10⁻⁵ M
Convert to mg/mL:
mg/mL = molarity × molecular weight = (1.71 × 10⁻⁵) × 66500 ≈ 1.14 mg/mL BSA
Example 2: IgG Sample with Dilution
Sample details:
- Absorbance: 0.42
- Dilution factor: 5
- Path length: 1 cm
- Extinction coefficient (ε): 210,000 M⁻¹cm⁻¹
- Molecular weight: 150,000 Da
Step 1: Calculate concentration of diluted solution:
M = A / (ε × l) = 0.42 / (210000 × 1) ≈ 2 × 10⁻⁶ M
Step 2: Convert to mg/mL:
mg/mL = 2 × 10⁻⁶ × 150000 = 0.30 mg/mL
Step 3: Adjust for dilution:
Original concentration = 0.30 × 5 = 1.50 mg/mL IgG
Example 3: Custom Protein
A researcher has an unknown protein with:
- Absorbance: 1.10
- Dilution factor: 2
- Path length: 0.5 cm
- Extinction coefficient: 50,000 M⁻¹cm⁻¹
- Molecular weight: 80,000 Da
Step 1: Calculate molarity:
M = 1.10 / (50000 × 0.5) = 1.10 / 25000 = 4.4 × 10⁻⁵ M
Step 2: Convert to mg/mL:
mg/mL = (4.4 × 10⁻⁵) × 80000 = 3.52 mg/mL
Step 3: Account for dilution:
Original = 3.52 × 2 = 7.04 mg/mL custom protein
Understanding the Formula: How Protein Concentration Is Calculated
Beer–Lambert Law
The calculator is based on the well-known Beer–Lambert Law, which states:
A = ε × c × l
Where:
- A = absorbance
- ε = extinction coefficient (M⁻¹cm⁻¹)
- c = concentration (M)
- l = path length (cm)
Rearranged for concentration:
c = A / (ε × l)
This gives molarity. To obtain mg/mL:
mg/mL = molarity × molecular weight / 1000
Why This Formula Works
Proteins absorb UV light at 280 nm due to aromatic amino acids like **tryptophan** and **tyrosine**. The extinction coefficient represents how strongly a protein absorbs light at this wavelength.
Sources:
- AAT Bioquest Protein Calculator
- OmniCalculator Protein Concentration Tool
- Standard molecular biology texts (e.g., Berg et al., "Biochemistry")
Common Pitfalls and What to Watch Out For
Using absorbance to calculate protein concentration is straightforward, but errors can easily occur if certain conditions aren't met.
1. Absorbance Too High (Above 1.2)
Readings above 1.2–1.5 often fall outside the linear range.
Fix: Dilute the sample until absorbance falls below 1.
2. Dirty or Scratched Cuvette
Fingerprints, scratches, or air bubbles distort absorbance readings.
Fix: Clean the cuvette thoroughly before use.
3. Incorrect Path Length
Micro-cuvettes may have shorter path lengths (0.2–0.5 cm).
Fix: Entering "1 cm" by accident will give incorrect results.
4. Wrong Extinction Coefficient
Each protein has a unique ε value.
Fix: Using the incorrect one changes the result significantly.
5. Buffer Absorbance
Buffers with additives (e.g., imidazole, DTT) absorb UV.
Fix: Always blank the spectrophotometer with the exact buffer used.
6. Contaminants or Precipitation
Turbid or cloudy samples scatter light → artificially high absorbance.
Fix: Centrifuge or filter the sample before measurement.
Glossary of Key Terms
Absorbance (A)
A measure of how much UV light the sample absorbs at a specific wavelength.
Extinction Coefficient (ε)
A constant describing how strongly a protein absorbs light at a specific wavelength.
Path Length (l)
The distance light travels through the sample, typically 1 cm.
Dilution Factor
How much the sample is diluted before reading (e.g., 10×).
Molecular Weight (MW)
The mass of one mole of protein, used for converting molarity to mg/mL.
Beer-Lambert Law
The fundamental principle relating absorbance to concentration: A = ε × c × l
Authoritative References
This Protein Concentration Calculator is built on widely accepted biochemical principles and validated using formulas from reputable sources:
AAT Bioquest Protein Concentration Calculator
Comprehensive tool for calculating protein concentration using various methods including UV absorbance and extinction coefficients.
Omni Calculator – Protein Concentration Tool
Educational resource explaining the Beer-Lambert Law application to protein quantification with practical examples.
Beer–Lambert Law (Standard Biochemical Reference)
Standard molecular biology texts (e.g., Berg, Tymoczko & Gatto – Biochemistry) provide foundational principles for UV spectroscopy and protein quantification methods.
These established methods ensure that your calculations are accurate, reproducible, and suitable for educational and laboratory use.
